1. Atomic Structure and Chemical Bonds
Chapter 6
Atomic Structure and Chemical Bonds

2. I. Atomic Structure
At the center of every atom is a nucleus containing protons and neutrons
Electrons travel in an area of space around the nucleus called the electron cloud
The electron cloud is mostly empty space and the exact location of any one electron cannot be determined

3. A. Electrons
Electrons have negative charges
Electrons travel in predictable areas, but it is impossible to know their exact location

4. B. Element structure
Each element has a specific number of protons, neutrons, and electrons
The number of protons and electrons is always the same for a neutral atom of a given element

5. II. Electron Arrangement
A. Electron energy
The different areas for an electron in an atom are called energy levels
Each energy level represents a different amount of energy

6. B. Number of electrons
Each energy level has a specific number of electrons it can hold
The farther an energy level is from the nucleus, the more electrons it can hold

7. To determine the maximum number of electrons that can occupy an energy level, use the formula, 2n2, where n equals the number of the energy level
Level 1 = 2 electrons = 2(12)
Level 2 = 8 electrons = 2(22)
Level 3 = 18 electrons = 2(32)
Level 4 = 32 electrons = 2(42)

8. = 32 e-
= 18 e-
= 8 e-
= 2 e-

9. C. Energy steps
Electrons in the level closest to the nucleus have the lowest amount of energy
Electrons farthest from the nucleus have the highest amount of energy and are the easiest to remove
- the closer a negatively charged electron is to the positively charge nucleus, the more strongly it is attracted to the nucleus

10. = 32 e-
= 18 e-
= 8 e-
= 2 e-
Energy

11. III. Periodic Table and Energy Levels
The atomic number for each element is the same as the number of protons in that element
The number of protons equals the number of electrons in a neutral atom
Therefore, the atomic number also tells you how many electrons are in a neutral element

12. IV. Electron Configuration
Atoms with a complete outer energy level are stable
Atoms with exactly eight electrons in an outer energy level are also stable
Each period in the periodic table ends with a stable element

14. V. Element Families
Each column of the periodic table contains one element family
Members of element families have similar chemical properties because they have the same number of electrons in their outer energy levels

15. A. Noble Gases
Elements in Group 8 have eight electrons in their outer energy level
Because their energy levels are stable, they do not combine easily with other elements
Helium is also stable because its single energy level is complete with only two electrons

16. B. Halogens
Elements in Group 7 need one more electron to obtain a stable outer energy level
The easier it is for a halogen to gain this electron, the more reactive it is
The reactivity of the halogens decreases down the group as the outer energy levels get farther from the nucleus
- the protons cannot pull electrons in as easily when they are farthest from the nucleus

17. C. Alkali metals
Elements in Group 1 each have one electron in their outer most energy level
The easier it is to remove an electron, the more reactive the atom is
The reactivity of the alkali metals increases down the group as the outer energy levels get farther from the nucleus
- less energy is needed to remove an electron from an energy level that is farther from the nucleus

18. VI. Electron Dot Diagrams
Because it is the outermost electrons that determine an atoms chemical properties, it is helpful to make models that show only those electrons
An electron dot diagram is the symbol for the element surrounded by as many dots as there are electrons in its outer energy level

19. A. How to write them
Dots are written in pairs on four sides of the element symbol
Group numbers 1 and 2 and 3-8 tell you how many electrons are in the outer shell for those elements

20. B. Using dot diagrams
Dot diagrams help show how many chemical bonds an atom can make
A chemical bond is the force that holds two atoms together
Atoms bond with other atoms so that each atom has a stable outer shell
- each atom likes eight electrons in its outer shell except for hydrogen and helium (they like two)

21. VII. Ionic Bonds-Loss and Gain
Atoms form bonds with other atoms in one of four ways:
1. losing electrons
2. gaining electrons
3. pooling electrons
4. sharing electrons with another atom

22. An ionic bond forms between two atoms when one atom losses an electron and another atom gains an electron

23. A. Ions – A question of balance
Sodium has only one electron in its outer level
The sodium atom loses an electron and becomes more stable with eight electrons in its outer level
An ion is an atom that has gained or lost an electron
Sodium lost an electron, so it now has one more proton than electron
Sodium is now a positive ion, Na+, because it lost an electron

24. Chlorine has seven electrons in its outer level
The chlorine atom gains one electron and becomes more stable with eight electrons in its outer level
Chlorine gained an electron, so it now has one more electron than proton
Chlorine is now a negative ion, Cl-, because it gained an electron

25. B. Bond formation
The positive sodium ion and the negative chloride ion are strongly attracted to each other
This attraction which holds the ions close together creates an ionic bond

26. A compound is a pure substance containing two or more elements that are chemically bonded
The compound made by sodium chloride is table salt (NaCl)

27. VIII. Metallic Bonding – Pooling
Metals form bonds with other metals by forming a shared pool of electrons
Metallic bonding allows metals to conduct electricity because the electrons are allowed to move from one atom to the next to transmit current

28. IX. Covalent Bonds – Sharing
The chemical bond that forms between nonmetal atoms when they share electrons
Shared electrons are attracted to both nuclei so each atom has a stable outer energy level some of the time
A molecule is the neutral particle formed when two atoms share electrons and have an equal number of protons and neutrons

29. A. Double bonds
When two pairs of electrons are involved in a covalent bond
ex. In carbon dioxide, CO2, the carbon atom shares two of its electrons with each oxygen atom

30. B. Triple bonds
Three pairs of electrons are shared between two atoms
ex. N2

31. X. Polar and Nonpolar Molecules
Some electrons are not shared equally between two atoms
Some atoms have a greater attraction for electrons than others do
An unequal sharing of electrons makes one side of the bond more negative than the other
A polar bond is a bond in which electrons are shared unevenly

32. A. The polar water molecule
In a water molecule, H2O, the oxygen atom has a greater share of the electrons in each bond
The oxygen end of a water molecule has a slight negative charge and the hydrogen end has a slight positive charge

33. Water is said to be polar; it has two oppositely charged ends like poles on a magnet
Molecules that do not have these uneven charges are called nonpolar molecules