1. Atomic Structure and Chemical Bonds
Why do atoms combine?
How elements bond

2. Why do Atoms Combine Atomic Structure
Center of atom is nucleus where protons and neutrons
found (almost all of atoms mass is found here)
Electron cloud
positive nucleus (protons) surrounded by a cloud of negative (electrons)
path of electrons are not predictable, rather can be found in predictable shells
for a neutral atom, there is equal number of protons and electrons…. But later we will see that sometimes atoms aren’t neutral

3. Electron Arrangement
Number and arrangement of electrons in the electron cloud are responsible for physical and chemical properties
Electron energy: position of electrons are found closer to nucleus first, then in shells farther away from nucleus
Only certain number of electrons can be found in each shell (or energy level)
First shell contains maximum of 2 electron (closest to nucleus)
2nd shell holds maximum of 8, 3rd, maximum of 18, fourth maximum of 32)
Have sub shells in 3rd shell and up, with maximum in sub shells of 8

4. Energy steps
Electrons in the 1st energy level contains lowest amount of energy
Electrons farther away have greater energy levels and are easier to remove from atom
To calculate the maximum number of electrons found in an energy level use the formula 2n2 ( n equals the number of the energy level)
It takes less energy to remove electrons that are farther away from nucleus, than those closer to nucleus

5. Periodic Table and Energy Levels
You can determine the number of electrons in an atom by looking at its atomic number
Number of electrons equal the number of protons in a neutral atom

6. Electron Configurations
As you move left to right in same row on periodic table, you notice the atomic number increases by one
1st period contains H and He..
H has one electron in outer shell and He has 2 electrons which fills its outer shell
2nd period
Lithium (atomic # 3) has 2 electrons in first shell and 1 electron in second shell
Be (At # 4) has 2 electron in first shell, 2 in second shell
B has 3 electrons in outer shell, C has 4, thru Ne which has 8 electrons and is full… it is stable

7. Electron configuration
On 3rd period on periodic table, it can hold a maximum of 18, but only 8 can be in outer shell
Na(sodium At # 11) .. 2 in first shell, 8 in 2nd energy level and 1 in outer shell
Period 3 ends with Ar which has 8 electrons in outer shell and is stable(doesn’t combine with others)

8. Magnesium configuration

9. Element Families
Groups or Families are represented by columns on periodic table depending on the number of electrons in outer shell
All in group I (Alkali metals) have 1 electron in outer shell
All in group II (Alkaline earth metals) have 2
Noble gases (group 18) are stable containing 8 electrons and are considered inert gases (completely unreactive)
Noble gases when pass an electric current through a vacuum bulb, emit light of various colors (neon light)

10. Halogens Group 17: called Halogens
Contain 7 electrons in outer shell, very reactive,
Atoms are always trying to have outer energy shells filled
Easier for Fluorine to pick up 1 electron to fill its outer shell than to lose 7 electrons, so it looks for an extra electron to fill its outer shell
F is most reactive atom in halogen group

11. Alkali Metals Alkali metals have one electron in outer shell
It is easier to lose the one electron than to pick up 7 electrons
Less energy is needed to remove electron farther away from nucleus, so Fr is most reactive atom in group 1

13. Electron Dot Diagram
Electron dot diagram is a shorthand showing the element and the number of electrons in outer shell
You need to know the symbol and the number of electrons in outer shell
Dots represent the number of electrons but they are written in specific order
Write 1 dot on top, next dot to right, bottom and to left…. Fifth dot pairs at top, then fills as electrons are added reaching 8 total

14. Using Dot Diagram
Electron Dot Diagrams show the elements and their outer configuration
By knowing what electrons would be needed to fill outer shell you can determine its ability to bond to other atoms
Chemical bonds is the force that holds two atoms together
This allows atoms to be more stable and resemble noble gases

15. How elements bond
Ionic Bonds… Loss and gain of electrons to fill outer shell
Bonding of atoms into compounds depend on outer shell being filled… Some atoms loose electrons, some gain electrons to become stable with 8 electrons in outer shell
Na is soft metal, very reactive, has one electron in outer shell
Cl has 7 electrons, very reactive, posonous gas
Cl will receive an electron from Na to become stable
Thus electrons are gained or lost to reach stable configurations

16. Ionic bonding of Sodium and Chlorine

17. Ions
Ions form when atoms loose or gain electrons and overall charge of atom is not neutral
Atoms which loose electrons (negative charge) become positive ions
Atoms which gain electrons become negative charged ions

19. Loosing and Gaining Electrons

20. Bond Formation Mg++ O -- MgO Si++++ Cl- SiCl4
Ionic bond: attraction which holds ions close together and a compound is formed NaCl
Na Cl NaCl
Mg++ O MgO
Si Cl SiCl4

21. Metallic Bonding--Pooling
Metals can bond to nonmetals such as NaCl MgO, LiF, MnO, KBr
Metals can bond to other metals in special bonding
Electrons aren’t held to other atoms, rather they move freely among all the ions in the metals which allow you to hammer, or stretch certain metals and allows conductivity of electric currents to flow

22. Covalent Bonding: Sharing of electrons
Rather than gaining or losing electrons, some atoms share electrons to form molecules (compounds are formed from ionic bonding)
Shared electrons are attracted to the nuclei of both atoms
No ions (charged particles) are formed
Gases in atmosphere form covalent bonds Cl2
Single bond

23. Double and Triple Bonds
Covalent Bond: CO2
Total Number of electrons : 16
Carbon does not follow the octet rule unless double bonds are formed.
Double and Triple Bonds
Carbon Dioxide CO2 N2

24. Polar and Nonpolar bonding
Atoms of some molecules can share electrons unevenly and cause one side of bond to have greater negative and positive pulls thus called polar covalent bonds like water H2O
O end of water molecule has slight negative charge and the H end has a slight positive charge (give molecule two opposite ends like a magnet)
Positive ends of H attracts the O ends
Gives water the special characteristics it has

26. Water Covalent Bond with polar bonds

28. Nonpolar Moecules
These are covalent bonds that do not have uneven charges and differ slightly in its ability to attract electrons
The triple bond of gases N2 is an example

29. Chemical Shorthand
Symbols for atoms are comprised of one, two or three letters
Can represent single letter C, O, N
Others represent elements name in another language K (latin for kalium meaning potassium)
First letter is capitalized second letter is small letter , Mg, Co

30. Symbols for Compounds
Utilizes symbols of atoms in compounds and the number of each atoms within the compound or molecule
NaCl refers to one atom of sodium and one atom of chlorine
H2O: 2 atoms of hydrogen and one atom of oxygen (the 2 represents a subscript indicating number of H atoms)

31. Chemical Formula
Chemical formula is a combination of chemical symbols and numbers that show which elements are present in a compound and how many atoms of each element are present
Ag2S, NH3, H2SO4, HCl, HNO3,
Na2CO3