Atoms can be joined to other atoms by chemical bonds

c) 2 (or more) atoms of different elements stuck together Atoms = smallest piece of an element Molecules = smallest piece of anything can be…. a) individual atoms of and element b) 2 atoms of same element stuck together c) 2 (or more) atoms of different elements stuck together

To show that atoms are bonded .. Write the element symbols right next to each other with no spaces in between NaCl Use subscripts to indicate how many atoms of each element are attached MgCl2 or K2O For 1 Mg atom with 2 Cl or 2 K with 1 O Na(SO4)2 subscripts outside () apply to all elements inside ()

Atoms with 8 valence e- are stable and don’t form bonds Why Atoms form bonds Atoms form bonds to become stable Stable atoms have full set of valence e- (valence e- are outer-most electrons) The max number of valence e- is 8 Atoms with 8 valence e- are stable and don’t form bonds Atoms want a full outer energy level

Atoms form bonds to become stable Atoms can from 3 kinds of bonds. 1) metal + non-metal forms ionic bonds 2) non-metal + non-metal forms covalent bonds 3) metal + metal forms metallic bond

Only He is stable with only 2 e-

How do you tell how many valence e- an atom has? The one’s place of the group number tells you the number of valence electrons EXCEPT for transition metals & He

Atoms can gain or lose electrons to get 8 valence e- In ionic bonds atoms do what-ever is easier (gain or lose) Metals lose e- to become positive cations Non-metals gain e- to become negative anions

Atoms with less than 4 valence electrons lose e- When the one e- in the outermost energy level is lost… The outer energy disappears Na becomes Na+

Atoms with more than 4 electrons gain e- Outer energy level full

After forming ionic bonds.. Lewis dot diagrams have either NO dots or 8 dots

Writing Ionic Formulas Write the element symbols (metal first) Add subscripts to represent how many atoms of each element are used Add oxidation numbers to show the charges on each atom Overall charge of compound = 0

In covalent Bonds Both atoms want to gain e- Atoms share e- to get full outer energy level Shared electrons count in the outer energy level of both atoms

Covalent bonds form: Between 2 or more NON-Metals Or Between NON-Metals and Hydrogen

Non-polar Bond If electrons are shared equally then the molecule that is formed is neutral

Polar Bonds have poles When one atom pulls harder on the e- the e- spends more time near that atom That end of the molecule is slightly negative

partial charges shown by δ

Covalent bonds can share 1 pair of electrons = single bond shown as 1 line C-C 2 pair of electrons = double bond shown as 2 lines C=C 3 pair of electrons = triple bond shown as 3 lines