Structure and Properties of Matter

 

Resources: Stanford University; Fordham Preparatory School; University of Colorado, Boulder; howstuffworks.com; UC Berkely; European Fusion Development Agreement.org; and Jefferson Labs

12.1 Structure and Properties of Matter

a. Identify, describe, and diagram the basic components within an atom (i.e., proton, neutron, and electron)
b. Know that isotopes of any element have different numbers of neutrons but same number of protons, and that some isotopes are radioactive
c. Differentiate between atoms, molecules, elements, and compounds
d. Click here to describe the role energy plays in the conversion from one state to another AND Click here to compare and contrast states of matter: Introduction to Solids, Liquids and Gases AND -Read up to "Smaller than Atoms"-from Heat Transfer and Thermodynamics, Subdomain 11.1
e. Discuss the physical properties of matter including structure, melting point, boiling point, hardness, density, solubility and conductivity
f. Recognize that all chemical substances are characterized by a unique set of physical properties
g. Define and calculate density, and predict whether an object will sink or float in a fluid
h. Explain that chemical changes in materials result in the formation of a new substance corresponding to the rearrangement of the atoms in molecules
i. Explain and apply principles of conservation of matter to chemical reactions, including balancing chemical equations
j. Explain the origin of heat energy changes that occur in chemical reactions
k. Describe factors that affect rates of chemical reactions
l. Distinguish among acidic, basic and neutral solutions by their observable properties
m. Describe the construction and organization of the periodic table
n. Based on position in the periodic table, predict which elements have characteristics of metals, semi-metals, nonmetals, and inert gases
o. Explain chemical reactivity using position on the periodic table
p. Predict and explain chemical bonding using element's positions in the periodic table
q. Recognize that inorganic and organic compounds (e.g. water, salt, carbohydrates, lipids, proteins, nucleic acids) are essential to processes within living systems
r. Explain the central role of carbon in living system chemistry

 

 

Identify, describe, and diagram the basic components within an atom (i.e., proton, neutron, and electron)

Symbols of the Elements

The Atomic Nucleus

Heavier atoms -Activity: beyond hydrogen. Note: when you click on "next" at the bottom of the page an applet will appear. When it loads, if there is still a blue field at the top, begin clicking at the lower right hand corner and go to the far left. Then above each of the elements of the periodic table you have unveiled, click again until an element doesn't appear. Do that all the way from left to right... as far up as you can go. NOW YOU ARE READY FOR THE ACTIVITY.

We have previously studied in the macroscopic world, how we can gain potential energy by doing work to go from a lower level to a higher level. When we return to the original level (especially if we were to jump off the higher area we had reached), our potential energy would completely change to kinetic energy (assuming no friction) as we fell toward the lower level. Kinetic energy is the energy that accomplishes work.

In the atom there is a corollary to this situation in the various energy levels of electrons around the nucleus. You have already learned about them in the previous unit. The s, p,d and f energy shells are energy sublevels within the major quantum numbers 1-7. s is the lowest energy sublevel, then comes p, then d and finally f (not shown on this animation.

1). Once you have made all elements visible, click on the periodic table elements at the far left (starting at hydrogen- H) and going down to potassium (K). At each point, compare the color of electrons and their positions around the nucleus. Do this in writing. You may wish to put your observations in a table.

Repeat for Be (Beryllium) to Calcium (Ca).

2) Then start again at Hydrogen and click on "Nucleus View". Click down the column, noticing what happens to the nucleus as you proceed down the column. Repeat again for the column beginning with Be (Beryllium)- Put your observations in writing: table or comparative description.

3) Return to the "Shell View" and begin clicking from K to the right until you reach Zn (Zinc) and compare the energy levels and position of electrons around the nucleus. Select "Nucleus View" and describe what happens to the nucleus from K to Zn. Make these observations in writing (table or comparative description)

3) Return to the "Shell View" and begin at Zn and click to the right until you reach Kr (Krypton). Compare the energy levels and position of the electrons around the nucleus. Select "Nucleus View" and do the same thing with Zn to Kr and tell what happens to the nucleus. Again, add your observations to a table or write a short paragraph detailing your findings.

4) Return to the "Shell View" and begin at B (Boron) to Ne (Neon) and compare the electrons to their position around the nucleus. Select "Nucleus View" and tell what happens to the nucleus from B to NE Table or written description.

5) Finally, return to "Shell View" and begin at He (Helium) and compare the electrons to their position around the nucleus as you go down the column to Kr. Do the same thing for Nucleus View as you go down the column. Report what happens to the nucleus. Do this in a table or by comparative descriptions of your observations.

1. Development of Atomic Theory

2. Development of the Atomic Model

Create an early model of an atom

Bohr's Atom- Development of Quantum Mechanical Model of Atom

Dual Nature of Electromagnetic Radiation- How small particles can act like waves

Dual Nature of Electromagnetic Radiation- Photoelectric effect

Dual Nature of Electromagnetic Radiation- Classic two-slit experiment with light (interference)

Dual Nature of Electromagnetic Radiation- Electrons and interference- see actual Novel Prize photograph of historic experiment below.

Two-slit interference pattern of electron particles: Nobel Prize winning experiment

 

 

3. Heisenberg's Uncertainty Principle- Introduces the idea of probability of movement and location of electrons. They are not bound by the mechanical principles that bind the macroscopic world.

 

4. Atomic Structure

 

Know that isotopes of any element have different numbers of neutrons but same number of protons, and that some isotopes are radioactive

Atomic Structure

Atomic Structure

Elemental Notation and Isotopes

The Strong Nuclear Force

Radioactivity and Half-life- When you click on the link to the left, you will come to a page that asks you to do an experiment. Read the instructions and click to see a sample experiment result to understand the content but don't do the experiment. Click on BACK ARROW (LEFT ARROW) ON THE TOP OF YOUR BROWSER AND READ ABOUT THE BACKGROUND OF RADIOACTIVITY AND HALF-LIFE below the empty table.

Some Uses of Radionuclides

 

 

 

Discuss the physical properties of matter including structure, melting point, boiling point, hardness, density, solubility and conductivity

Structure of Matter- 10 pages

Melting Point

Boiling Point (phase changes) and states of matter

Boiling Point of Quarks

Hardness

Density: The mass of any material divided by the volume it occupies

Density of air and effect on humans

Four ways a conductor can be classified-

Most people think of conductors as substances that give very little resistance to the passage of an electric current. Although this is true, the decreased conductivity of semi-metals and the great resistance to the passage of electric currents of insulators still classify them as a type of conductor.

Conductivity of metals- Check out the relative differences in metals to serve as conductors

Solubility-Brief tutorial

 

 

Recognize that all chemical substances are characterized by a unique set of physical properties

The physical structure of the world and every object of matter in its atmosphere, upon and beneath its surface and within the depths of its oceans is made of atoms, ions, and molecules. Each chemical substance has a specific structure and specific physical and chemical properties because of the kinds of atoms that make them up, the way the atoms are held together (ionic, hydrogen or covalent bonding) the closeness of packing of the atoms or molecules, their three dimensional orientation in space and even the order in which the atoms are put together within the chemical substance. This difference in structure carries over to differences in function.

 

Define and calculate density, and predict whether an object will sink or float in a fluid

Density: The mass of any material divided by the volume it occupies

Density Experiment what makes things float and sink in a fluid?

1) Download one of the two handouts at the top of the shockwave multimedia activity.

2) Log the mass of each object and its volume that it occupies into the form and calculate the density of each object by dividing the mass by the volume. In the right-hand column labeled ranking, rank the objects from the least density to the highest density.

3) Set the current density to the density of water... 1g/mL or 1g/cm^3.. Predict which objects float (F) and which will not float (NF).

4) Describe the conditions of an object to have it float in water.

5) Now decrease the density of the fluid to its lowest possible value (this is done by moving the slider under the water to the far left. Place ALL OBJECTS INTO THE FLUID.

6) Predict at what density each object will float AS YOU GRADUALLY INCREASE THE DENSITY OF THE FLUID. Test your predictions by slowly increasing the density of the fluid and as each new object begins to float, write down the density of the fluid.

7) Create a general statement about what will make any object float in a fluid, irrespective of what the relative density is of the object and fluid.

 

Explain that chemical changes in materials result in the formation of a new substance corresponding to the rearrangement of the atoms in molecules

Chemical Changes

What is happening in a chemical reaction to make these changes?

 

 

Explain and apply principles of conservation of matter to chemical reactions, including balancing chemical equations

 

Law of Conservation of Mass - States that the amount of mass in the universe is CONSTANT

This means the atoms that exist today are essentially the same ones that existed thousands and millions of years ago. The atoms in use today have been recycled time after time. Everyone has been recycling since the beginning of time.

It also means that in chemical reactions like the oxidation of zinc seen to the left, that even though new chemicals are formed, the overall mass stays constant.

To be able to numerically understand the concepts above as well as those below, you need to understand the concepts of atomic and formula mass and percent composition.

The atomic mass is the average of all isotopes of an atom and is found below the symbol and name of the atom in the periodic table. For example, calcium (Ca) atomic mass is 40.078 atomic mass units (u). The formula mass is the sum of all the masses of the atoms in the formula of the compound. Practice these concepts in the link below.

 

Formula Mass and Percent Composition

 

Gram Formula Mass

Percent Composition- Instruction and Practice 1

 

Law of Definite Proportions- (Joseph Poust): Different samples of a pure compound always contain the same elements in the same proportion by mass.

Law of Multiple Proportions- The law of multiple proportions states: If two elements combine to form more than one compound, then the ratio of the weights of the second element (which combines with a FIXED weight of the first element) will be small whole numbers.

These laws and observations led to Dalton's Atomic Theory

Dalton's Atomic Theory

 

 

Explain the origin of heat energy changes that occur in chemical reactions

Energy and Rate of Reaction

Chemical Reaction Rates- and the factors that control them

Types of Chemical Reactions

Endothermic and exothermic reactions

Enzymes in chemical reactions: examples of catalysts- Basic information

 

ENDOTHERMIC REACTION ANIMATION: Letters with blue colors in the animation below represent low energy atoms, red colored letters being animated represent HIGH energy atoms. Change in colors: blue to red means that the atoms are gaining energy; change from red to light red/orange means losing some of the energy.

ENERGY ABSORBED IS THE SAME AS THE ENERGY OF REACTION

 

EXOTHERMIC REACTION ANIMATION: Letters with blue colors in the animation below represent low energy atoms, red colored letters being animated represent HIGH energy atoms. Change in colors: red to blue means that the atoms are losing energy; change from light red/orange to red means gaining some of the energy.

ENERGY RELEASED IS THE SAME AS THE ENERGY OF REACTION

 

Reaction Rates

Chemical Kinetics- advanced discussion (select from menu of concepts you are weak in or proceed sequentially. Allows you to perform experiments through marvelous applets.

Chemical Equilibrium- advanced discussion

 

 

What is a chemical reaction?

Examples of chemical changes

Chemical equations of chemical reactions

 

Writing formulas of ionic compounds

The animation to the left teaches you how to write the formulas of ionic compounds. There are three objects that control the animation. DO NOT CLICK THE START BUTTON UNTIL YOU HAVE READ THE FIRST EXAMPLE DOWN TO THE INSTRUCTIONS: CLICK BUTTON TO SEE

1) The large green circle STARTS and CONTINUES the animation. It will also will reset it when it is at the end.

2) The small red circle to the left that will stop the animation at any time (Press green circle to begin it again) and

3. The left arrow reverses the animation by 5 frames. To restart the animation click on the green circle.

FIRST EXAMPLE: When you click the start button, you will see the metal ion potassium (K) and nonmetal chloride ion (Cl) move together. The electric charge of potassium ion is 1+ (this is its oxidation number) and the electric charge of chloride ion is 1- (this is its oxidation number). Go ahead and click on the start button now.

The next step is to cross over the oxidation numbers. The oxidation number of chloride becomes the subscript to potassium and the oxidation number of potassium becomes the subscript of chloride. The only problem is that the subscripts have a positive and negative sign on them. THESE SIGNS ARE DROPPED AND THE FORMULA OF POTASSIUM CHLORIDE IS K1Cl1.

CLICK BUTTON TO SEE

Whenever you have the situation of the identical subscript in both ions no matter what the numbers are, they are dropped (like simplifying math) and the actual formula used is KCl. Potassium and chlorine is combined on a one-to-one ratio.

CLICK BUTTON TO SEE

SECOND EXAMPLE: DON'T CLICK GREEN BUTTON UNTIL YOU GET TO CLICK BUTTON TO SEE: We will now look at the combination of calcium ion Ca (2+) (this is its oxidation number) and nitride ion (N)(3-) (this is its oxidation number. Notice that the oxidation numbers are not equal, so they won't be dropped. The same principle applies... the oxidation numbers cross over and the signs are dropped. Calcium nitride is formed.

You will be clicking once to see the two ions together. The second time you click the button you will see the crossing over and the charges drop.

CLICK BUTTON TO SEE

THIRD EXAMPLE: Ammonium ion (NH4) (1+ is its oxidation number) will be combined with sulfate ion (SO4) (2- is its oxidation number). Both of these ions are polyatomic ions (ions with multiple atoms). See the sulfate ion in three dimensions at the bottom of this page. It is the three-dimensional icon at the bottom of the page.

Notice that both the polyatomic ions have parentheses around them. The reason will be explained shortly. When you click on the button, you will see both ions and their charges come together. Click a second time and you will watch the crossing over and dropping of the POSITIVE AND NEGATIVE SIGNS as done above.

CLICK ON BUTTON TO SEE

FOURTH EXAMPLE: The ammonium ion has the subscript 2. This means there are 2 ammonium ions for every single sulfate ion. The ammonium ion has a parenthesis around it so that it is clear that the number 2 tells HOW MANY OF THESE IONS THERE ARE. The sulfate ion has the subscript 1. THERE IS NO NEED TO HAVE THE SUBSCRIPT 1. The subscript is dropped and so is the parenthesis on the sulfate. The 1 is understood and does not need to be written. Had there been a subscript of 3, the parenthesis could not be dropped because that would tell how many sulfate ions there are in the formula.

CLICK BUTTON TO SEE

CLICK THE BUTTON ONE MORE TIME. It will reveal a practice assignment. You will see the oxidation numbers of each of the metal and nonmetal ions. The answers to each question will be in text boxes below the question. COMPLETE PRACTICE ASSIGNMENT BELOW (QUESTIONS)

QUESTIONS

Write the formula for each of the following.

Check to check your answers below

 

Naming Compounds

Naming Chemical Compounds

Naming Chemical Compounds- Practice

Naming Acids: Scroll to bottom of page

 

Balancing Chemical Equations

Balancing ionic equations with polyatomic ions

Balancing equations where water is a product (combustion reactions)

Balancing by overview

Types of Chemical Reactions- practice balancing all equations

Decomposition Reactions

Synthesis (Combination) Reactions

Single Replacement Reactions

Double-Replacement Reactions

Avogadro's Number

Practice problems: writing chemical formulas, identifying reaction types and balancing chemical equations. If you can do this you are now in advanced status

 

Balancing oxidation-reduction reactions (Advanced)

How are redox reactions different?

Oxidation states

Is it a redox reaction?

Half reaction

Reduction or oxidation?

Practice with assigning oxidation states

Balancing redox reactions

 

 

Distinguish among acidic, basic and neutral solutions by their observable properties

What is an acid and a base?

Properties of acids

Properties of bases

Strong acids and bases

Solubility and dissociation

Overview of pH

pH Box

Calculator use with pH box

The pKa box

Weak acids and bases

pH of strong acids and bases

Weak acids

Weak bases

The 5% rule

pH of weak acids and bases

Buffers and pH of buffers

Titration

Titration math

 

 

 

Describe the construction and organization of the periodic table

 

Classification of Matter

Discovery of the Element

Occurrence of the Elements

Periodic Table: Information about elements - Includes distribution in the Earth

4. The Periodic Table- Background

 

 

Based on position in the periodic table, predict which elements have characteristics of metals, semi-metals, nonmetals, and inert gases

 

a) Metals and Nonmetals-

Metals to the left of the DARK BLACK stair-step line including inner transition elements

Nonmetals to the right of the DARK BLACK stair-step line

Transition Elements (Include the B families and inner transition elements- for more details, see below)

Semi-metals (also called metalloids) in light yellow- Elements that have both metallic and nonmetallic properties. Excluding aluminum which is ALL METAL, they are on either side of the metal/nonmetal dividing line.

b) Families- vertical columns on periodic table

Hydrogen- Nonmetal (diatomic gas in nature) but placed here on periodic table because of electron configuration (oxidation number). Oxidation number is 1+

1A Alkali Metals

2A The Alkaline Earth Metals

Neon: has an electron structure similar to the 2A elements but is a not a metal... it is a nonmetal gas and is very stable and is part of the family of Nobel Gases. It has no oxidation number.

B families- Transition metals (elements)

3A Aluminum Family

4A Carbon Family

5A Nitrogen Family

6A Oxygen Family

7A The Halogens

8A Noble Gases

Diatomic Gases- notice the location of the atoms on the periodic table

Semi-metals or metalloids

have properties of both metals and nonmetals and are in light yellow on either side of DARK BLACK stair-step line.

 

c) Periods- horizontal rows represent the 7 major quantum numbers (energy levels [n] or areas outside the nucleus for electrons of different energies.)

Period 1: H and He (H is not a metal but has the electron configuration consistent with Alkali Metals)

Period 2: Li, Be, B, C, N, O F, NE

Period 3: Na, Mg, Al, Si, P, S, CL, Ar

Period 4: All elements beginning at K through Kr

Period 5: All elements beginning at Rb through Xe

Period 6: All elements beginning at Cs through Rn

Period 7: All elements beginning at Fr through the newer elements synthesized.

 

d) Radius of Metal and Nonmetal atoms and Ions: A Comparison

When metal atoms lose electrons to become stable ions, they shrink significantly. When nonmetal atoms gain electrons to become stable ions, they expand. Why does this occur? See animation below:

 

 

SUMMARY: The electron leaves sodium ATOM so the atom will achieve stability (it will be captured by a non-metal).

When it leaves there are 11 protons and 10 electrons... There is a net charge in the atom of 1+

The electrons are drawn toward the positive source.

The THREE DIMENSIONAL SPACE OF THE METAL ION IS NOW SIGNIFICANTLY SMALLER THAN THE SODIUM ATOM.

 

 

 

 

SUMMARY: Three electrons enter the phosphorous ATOM so it will achieve stability (the electrons come from metal ions).

Prior to entering there were 15 protons (+) and 15 electrons (-) in the phosphorous atom. After they enter, there are three more electrons than protons in the atom so the net charge of the atom is negative (3-).

Since similar charges repel each other, the electrons are pushed away from the protons.

The THREE DIMENSIONAL SPACE OF THE NON-METAL PHOSPHIDE ION IS NOW SIGNIFICANTLY GREATER THAN THE SPACE WITHIN THE PHOSPHOROUS ATOM.

 

 

 

Explain chemical reactivity using position on the periodic table

Predict and explain chemical bonding using element's positions in the periodic table

Electron Configuration and Valence Electrons

 

a) Writing Electron Configurations

The animation below teaches you how to write electron configurations.

1. The first electron configuration that will be written is that of hydrogen (with the symbol, H- see below.) The atomic number of Hydrogen is 1. This means there is 1 proton and 1 electron in the atom. We are only interested in the atom. CLICK ONLY ONCE ON THE BUTTON ABOVE THE H (Hydrogen). Did you see the ball move to the 1s position. The ENERGY sublevel "s" can hold up to 2 electrons only, but hydrogen has only one electron... Therefore, only one electron can be placed into the s-sublevel. There are no more electrons that can be placed in the atom. The electron configuration ends in 1s1 (see below).

2. The second electron configuration is for helium (He). Helium has an atomic number of 2. There are two electrons and two protons in the atom. We only worry about the electrons. CLICK ONLY ONCE ON THE BUTTON ABOVE H. Did you see the ball move to the same 1s position? But look at the electron configuration of He in the animation... it is 1s2. Since there is a total occupancy space of 2, we filled BOTH electrons into the 1s sublevel. The electron configuration ends in 1s2.

3. The third electron configuration is K or potassium. The atomic number of K is 19... meaning 19 electrons (and of course an equal number of protons). We must now put the electrons into the different sublevels. They fill in a consistent and easily understandable order.

Remember that the s-energy sublevel holds a maximum of two electrons. The p-energy sublevel holds a maximum of six electrons. The d-energy sublevel holds a maximum of ten electrons. The f-energy sublevel holds a maximum of fourteen electrons.

You can add less than the total number potential of electrons per sublevel BUT ONLY WHEN YOU HAVE A LOWER NUMBER OF ELECTRONS TO COMPLETE THE FILLING OF THE LAST SUBLEVEL. For potassium, the last sublevel filled is 4s and there is only one electron left to place...so it is 4s1.

Be aware that the electrons in the s-sublevels have the least amount of energy. The energy of the electrons increases until it gets to those in the f-sublevels that have the greatest energy.

NOW CLICK ONCE ON THE BUTTON in the animation. It will automatically stop at the first sublevel. Observe the course it takes and pay attention to the number of electrons that are left to fill the the entire atom. CLICK ONCE AGAIN. The process repeats itself until you complete the electron configuration. You will know you have arrived at completion when the ball becomes transparent.

4. Sc (scandium) is next. Repeat the process described above. The last sublevel filled is 3d1.

5. I (iodine) is next. Repeat the process. The last sublevel filled is 5p5.

6. Yb (ytterbium) is the last example. Repeat the process. The last sublevel filled is 4f13

 

b) The electron configuration of each atom determines not only its properties but also how it will behave in chemical reactions.

 

c) The periodic table gives the key to remember the last energy level (quantum level) (n), orbital (s, p, d, f) and number of electrons in the last energy level.

WHY IS STABILITY ACHIEVED IN METALS BY THE LOSS OF ELECTRONS AND IN NONMETALS BY THE GAINING OF ELECTRONS ?

a) Remember from the discussion above

 

Strontium atom electron configuration (example of a metal)

1s22s22p63s23d104p65s2

The last level of strontium atom is 5s2 which puts strontium in the IIA family. The IIA family has two electrons in its outer energy sublevel. Write down which is the energy sublevel with the highest energy and click on the field below to see if you are right.

Which will require least work for the atom to become stable: Will it gain six electrons to gain 8 electrons (2+6 = 8) or lose two electrons (to have a total of 8 electrons in its outer energy level)?

 

Bromine atom electron configuration (example of a nonmetal)

1s22s22p63s23d104p5

Write down which is the energy level with the highest energy and click on the field below to see if you were right.

Which will require least work for the nonmetal atom to become stable: Will it gain one electron (to complete 8) or lose nine electrons to gain a stable 8 electrons in the outer energy level.

See Octet Rule: Chemical Bonding

 

Activity 1:: WRITE THE FOLLOWING INFORMATION:

a) Which area of periodic table is filling the s orbital last as the outermost layer of the atom,
b) Which area is filling the p orbital last.
c) Which area is filling the d orbital last and
d) Which area is filling the f orbital last.
Answers to choose from: 1) Area to the left of the Transition Elements 2) Area to the right of the Transition Elements, 3) The Transition Elements themselves and 4) The Inner Transition Elements (Lanthanides and Actinides).

 

Activity 2: WRITE THE FOLLOWING INFORMATION:

The oxidation number and number of electrons in the outer energy level in all of the A Families and the name of each of the A families.

 

Trends in the Periodic Table

a) Why the trends exist. Example: size of atoms down a family

Family I A (name of atoms and period number)
Visual representation
What is happening?

Hydrogen(H) Period 1

The first quantum number (Period) (1) represents atoms that have only one energy level (represented by the single line circle). This also is the outer energy level. It is very close to the nucleus represented by the red circle. Electrons in this level are held tightly.. This nucleus has one proton and a positive charge of 1+
Lithium--(Li) Period 2
The second quantum number represents atoms that have two energy levels like Lithium. The outer energy level is farther away from the nucleus. Note that the nucleus size is increasing because this nucleus has 3 protons and 4 neutrons. That means the positive nuclear charge has increased threefold. Electrons in the outer energy levels are held less tightly than those in period 1.
Sodium--(NA)-- Period 3
The nucleus of the third quantum number is larger still and has three energy levels as sodium has. This nucleus now has 11 protons and 12 neutrons. There is 11 times the positive nuclear charge compared to period 1. Note that there are now two energy levels of electrons between the nucleus and the outer level. The electrons are held less tightly than those in Period 2.
Potassium (K) Period 4
The atoms in the fourth quantum level have 4 energy levels of electrons around them. The nucleus is larger still (19 protons, 20 neutrons). There is a nineteen-fold increase in the positive nuclear charge. The electrons are held less tightly than those outer electrons in Period 3. Note that there now are THREE energy levels of electrons between the nucleus and the outer energy level.
Rubidium (Rb) Period 5
The atoms of the fifth quantum level (period 5) have 5 energy levels around them. The nucleus is even bigger (37 protons and 48 neutrons). There is a 37-fold increase in positive nuclear charge compared to period 1. The outer electrons are held MUCH less tightly than those in period 4 as represented by the increased space.. Note that there are now four energy levels of electrons between the nucleus and the outer energy level of electrons.
Cesium (Cs) Period 6
You fill in details
You fill in details.
Francium (Fr)Period 7
You fill in details
You fill in details.

As one looks at the atom down most families the atoms increase in size as shown above. It may seem strange because one would think that the large increase in nuclear charge (positive charge) would actually tend to cause a greater attraction to the electrons drawing the electrons closer to the nucleus... making them smaller. But it doesn't happen.

The greater number of energy levels that occur between the nucleus and the outer level gives a "shielding effect" against the strong positive charges of the nucleus. THEREFORE, ATOMS INCREASE IN SIZE DOWN A FAMILY BECAUSE OF THE INCREASING INFLUENCE OF THE SHIELDING EFFECT on the outer energy levels of the atom.

 

b) Why the trends exist. Example: size of atoms across a period.

Period 4

Visualization

19

Potassium

20

Calcium

21

Scandium

22

Titanium

23

Vanadium

24

Chromium

25 Manganese

26

Iron

27

Cobalt

What is Happening and names of atoms Potassium has 19 protons and 19 electrons Calcium has 20 protons and 20 electrons Scandium has 21 protons and 21 electrons Titanium has 22 protons and 22 electrons Vanadium has 23 protons and 23 electrons Chromium has 24 protons and 24 electrons Manganese has 25 protons and 25 electrons Iron has 26 protons and electrons Cobalt has 27 protons and electrons

As one looks at the size of the atoms across a period we see a gradual decrease in the size of the atom. This is because for each increase in "1" in atomic number, the next atom has one more proton and one more electron. This maintains the charge balance at 0... but the nuclear charge keeps on getting bigger. As a result of the increased atomic charge the electrons are drawn toward the nucleus and become smaller. The outer electrons are held more and more strongly as you move to the right along a quantum number or period.

The trends in the periodic table along the period or quantum number (from left to right) are due to INCREASED NUCLEAR CHARGE.

 

c) Specific Trends:

i) Ionization Energy: The energy required to remove the outer electrons of an atom (those in the outer energy levels of the atom)

The ionization energy INCREASES to the right across a period (the outer electrons are held more tightly because of the increased nuclear charge) and DECREASES down a group or family (the outer electrons are held less tightly because of the increasing shielding effect).

ii) Electronegativity: Electronegativity is the tendency of an atom to attract electrons to itself when bound to another atom. These values are measured are measured when two atoms are combined. The actual electronegativity of each element of the bond is subtracted from each other (leaving a positive number as an answer).

This difference between electronegativity values of each individual atom tells whether they will be bonded covalently or by ionic bonding.

Click here to see the relationship of electronegativity differences and type of bonding (covalent, ionic, polar covalent.... and relationship to the periodic table)

iii) Electron Affinity: Electron affinity is the ability of an atom to attract an pull the electrons from another atom to itself. Nonmetals to the right of the periodic table should have a high ability to pull electrons into themselves because they form negative ion.

Electronegativity and Electron affinity DECREASE as one goes down a group of family and INCREASE from left to right across a period or quantum number. This confirms the supposition in the paragraph above.

iv) Metal and nonmetal properties: Nonmetallic properties increase from left to right across periods and from the bottom to the top of families in the periodic table. Metallic properties decrease from the left to the right across periods or quantum numbers and from the top to the bottom of families. This follows the change in the electron affinities of the atoms.

 

 

Recognize that inorganic and organic compounds (e.g. water, salt, carbohydrates, lipids, proteins, nucleic acids) are essential to processes within living systems

Explain the central role of carbon in living system chemistry

 

Nucleic Acids - backbone of both nucleic acids and carbohydrates associated with DNA and RNA

Carbon Cycle- formation of carbon atoms/carbohydrates through photosynthesis using carbon dioxide and the source of all energy (ATP)

Amino Acids in proteins- The backbone of all proteins.

Carbohydrates- Source of high energy carbons, structure of cell walls in living things

Lipids- Structural components of biological membranes, provide energy reserves, predominantly in the form of triglycerols Both lipids and lipid derivatives serve as vitamins and hormones.

Salt

Water

 

Allotropes- Definition plus you will be able to see the three-dimensional structure of three allotropes of carbon and physically rotate them.

 

 

 

 

Go back to Electricity and Magnetism

 


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