Download Valence electrons and Lewis Dot Structures

Valence electrons and Lewis Dot Structures

The electrons in the outermost shell are the
___________ ____________ the
electrons on an atom that can be gained or
lost in a chemical reaction.
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d and f electrons don't do much in chemical
reactions, so they can be ignored.
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Valence electrons are the ____ and ____
electrons in the highest energy level.
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Example: Ga: [Ar] 4s2 3d10 4p1 Gallium has 3
electrons available for bonding.
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Determine the number of valence electrons
available in Si, Mn, Sb, and F.

The _________ _________ basically says
that an atom wants to have 8 electrons in
the s and p orbitals. It will gain, lose or
share electrons in order to achieve this
configuration.
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G.N. Lewis came up with a way to show this
called Lewis Electron Dot Structures, or
Electron Dot Diagrams. They are used
interchangeably.

Write the symbol. Place one dot for each
valence electron. Double up as you come
around.
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Example: Si, Mn, Sb, F
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Can be used to show how electrons are
shared in bonding. Example: H2O, CH4, CO2
Formulas!

What is a chemical symbol?

used in writing chemical formulas

A chemical formula is a type of notation made
with #s and chemical symbols
1. tells you composition of a compound
2. tells you the number of atoms in a molecule

A _______________ can be a single atom, 2
or more atoms of the same element, or a
group of atoms of different elements that have
combined to form a compound.

a single atom molecule is called
______________ noble gases only

2 atoms of the same element is called
_______________(only 7)

H2, O2, N2, Cl2, F2, Br2, I2  always travel in
pairs.

To write the chemical formula, write the # of
atoms of each element as a subscript after its
symbol.

1 is understood, but never written  He, not
He1

ex. P4, S8, Xe, O2, Kr, etc.
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For compounds, formulas tell you how many
atoms and what kind

ex. H2O, CO2, CH3CH2OH, etc.
Ionic Substances
 There are 2 basic types of compounds:
Molecular and Ionic.

Each has a different naming system

Must be able to tell them apart

Usually, a compound formed by a metal and a
nonmetal is _________, and a compound
formed by two nonmetals is ____________.

exceptions will be discussed later

Which of the following will be ionic? CaF2 CH4
FeCl3 Br2 CO2 SrO

atoms in a free (unbonded) state have equal
numbers of protons and electrons 
electrically neutral

When a metal and a nonmetal combine
chemically, they form an ionic bond.

Means that one or more electrons are
____________ from the metal to the nonmetal
(no longer neutral) these are now ions

Atoms that gain electrons become
____________ ions

Atoms that lose electrons become
_____________ ions

An ionic compound is the result. Ex. NaCl,
MgCl2

To write an ion, write the symbol of the element
followed by a superscript that tells the charge.
Ex. Na+ Mg2+ Cl-
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General Rules:
Column 1: 1+
Column 2: 2+
Column 13 : 3+
Column 14: 2+ or 4+
Column 15: 3Column 16: 2-
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Column 17: 1Column 18 has a charge of zero.
Ionic formulas
A few definitions:
 Positive ions are called _________ (made by
metals)

Negative ions are called __________ (made by
nonmetals)

Ionic compounds with only 2 different elements
are called ____________________________.
Ex. MgCl2 KI
Rules for writing Binary formulas:
1. Write the symbols down, metal first.
2. Determine the charge of each ion, either from
its position on the PT or a chart like 7-8 on p.
155 (PH book)
3. Use subscripts to make the total positive
charge = total negative charge Must be
electrically neutral.

MgF2 Na2O Al2S3 KBr

A group of atoms of more than one element
that carries a charge is called a
____________________ ion.

act like a single atom (like your fingers act as a
single unit)

Ex. OH- NH4+ CN-
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So we need one more rule
4. When using subscripts with polyatomics, put
the polyatomic ion in parenthesis if you need
more than one and put the subscript outside
Ex. Al2(SO4)3
Mg(OH)2
MgSO4