The Structure of Matter

1
The Structure of Matter
2
Compounds Molecules
Chemical bond
attractive force that holds atoms or ions together

• chemical formulas show the type s of atoms
  or ions making up the simplest unit of the
  compound

Chemical structure shows the bonding w/in a
compound
Chemical structure
ex.
arrangement of bonded atoms or ions w/in a
substance
3
Models of Compounds

• used to help you see a compounds structure by
  showing how atoms or ions are arranged in the
  compound

ex.

• structural formulas show the structures of
  compounds using only chemical symbols to
  represent atoms

Ball stick

• space-filling models show the space occupied by
  atoms

4
Bonding
What holds bonded atoms together?

• atoms bond when their valence electrons interact
  (to get a full outer shell)

a bond formed by the attraction between
oppositely charged ions
Ionic Bonds
electron transfer

• atoms of metal elements (ex. Na) form a
  positively charged ion

• atoms of
• nonmetal elements (ex. Cl)
• form a negatively charged ion

5
Ionic Bonds

• to fill the outermost energy level, electrons
  are transferred

• one atoms gains what the other loses both
  usually have full outer shells

• the result is one cation () one anion (-)

• the oppositely
• charged ions
• attract each other form an ionic bond

6
Ionic Bond Formation
Step 1 show the electron dot diagrams for both
the metal and the nonmetal Step 2 show the
transfer of electron(s) that will take place you
might need more than one atom Step 3 show the
ions that form as a result of this exchange of
electron(s) Step 4 show the chemical formula
for the molecule of the new compound that forms
For example react sodium with chlorine
NaCl
7
Bonding (cont.)
Structural Formula
shows how atoms are connected in the molecule
that forms

• a single line drawn between 2 atoms indicates
  the atoms share 2 electrons joined by one
  covalent bond

• atoms may share more than one pair of electrons

8
Bonding (cont.)
What else holds atoms together?
Covalent Bonds
a bond formed when atoms share pairs of valence
electrons

• often formed between nonmetal atoms

• have low melting points

ex. H2O
Hydrogen atoms and an Oxygen atom want to bond
Hydrogen atoms each need 1 e- and the Oxygen atom
needs 2
If the Hydrogen atoms each share their 1 e- with
the Oxygen atoms 6 e-, then both atoms together
have full outer shells
9
Covalent Bond Formation
Step 1 show the electron dot diagram for each
nonmetal Step 2 show the sharing of electrons
by circling the shared pair Step 3 show the
resulting lewis structure that is formed also
show the structural formula Step 4 show the
chemical formula
For example react hydrogen chlorine

HCl

H Cl
10
Comparison
11
Electron (Lewis) Dot Diagrams
symbol for the element surrounded by as many dots
as there are electrons in the outer energy level
How to
1. written in pairs on four sides of the element
symbol
2. write one dot on the top, then work your way
around
3. then begin making pairs
12
Hydrogen Bonding

• water exhibits this type of bonding because of
  the hydrogen the (electronegative) oxygen

• O pulls the shared e- away from the H atom

• leaving the H proton exposed to attract the
  negative parts of other polar molecules