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Compounds,
Diatomic
molecules,
ions,
electron dot
diagrams,
and
Formulas
Let’s Review:
• Elements- pure substance made of only 1
kind of atom (found on periodic table)
• Atom- smallest unit of an element that
maintains the properties of that element
--protons, neutrons, electrons
• Compounds- pure substance made of two or
more different elements that are chemically
combined.
Compounds
• Each has its own formula
Examples:
potassium bromide
KBr
Formulas
• Example: Aspirin—C₉H₈O₄
• Use symbols & subscripts
• Subscripts
--tells number of atoms of each element
--right of symbol, below the line
--counting numbers 2 or above
--1’s are ALWAYS understood
Formula
• Shows ratio of atoms of elements—must
be written in simplest form
Example:
H2O (water)
ratio hydrogen atoms to oxygen atoms
2:1
Another example:
• CO2
ratio 1:2
carbon dioxide
• CO
ratio 1:1
carbon monoxide
• C₂O₄ ratio 2:4
Is not in simplest form
Diatomic Molecules
• Substance composed of only 2 atoms
may be 2 of same element (0₂) or 2
different elements (CO)
• 7 diatomic molecules found on periodic
table—(H, O, N, I, F, Cl, Br)
7 up rule…do you see it?
Isotope
• An atom of element with different mass
number
• Has same # of P+ but different # of n⁰
• An atom of carbon has 6 neutrons
• An isotope of carbon: Carbon-14 has 8
neutrons
• Write name or symbol or element with
dash then mass number.
– Carbon-14
– C-14
Electron Dot Diagrams
An electron dot diagram is the chemical symbol
surrounded by dots which represent the number
of valence electrons.
.
.C..
Carbon’s chemical symbol is C. Carbon has
4 valence electrons. This is the electron dot
diagram for carbon.
Ions
• An atom with a charge
• Due to the loss or gaining of a valence
electrons
• Will form ionic bonds
• Polyatomic Ions- group of charged atoms
that behave as a single atom
– Example: NO₂ Nitrite 1-
Ions
• Oxidation number- charge of ion
• If atoms have less than 4 VE, will lose
valence electron(s) & become positively
charged ion called cation.
• If atoms have more than 4 VE, will gain
enough valence electron(s) to fill outer
energy level & become negatively
charged ion called anion
• Exactly 4 VE- tend to do both depending
on circumstances