deals with letters/symbols from the periodic table to describe substances instead of words example:...
TRANSCRIPT
Deals with letters/symbols from the periodic table to describe substances instead of words
EXAMPLE:
Molecular formulas
Molecular formulas
WordsWords
Molecular Formulas
Molecular Formulas: Recall elements can combine to
form compounds
But when atoms combine, they do so in specific ratios
For example: Water, H2O Combines 2 Hydrogens for every 1
Oxygen
An atom wants to be stable
To be stable, an atom must have a full outer electron shell (8 electrons)
Octet Rule
Atoms combine together, forming bonds, to fill their outer electron shell
Molecular Formulas:
The number of bonds that an atom can form is termed the valence
Molecular Formulas:
Atoms in Family
Valence
1 1
2 2
3 3
4 4
5 3
6 2
7 1
Number of
bonds each atom can
make
How many bonds would an element in the families below make?
a) Family 2
b) Family 5
c) Family 7
d) Family 8
2 bonds
3 bonds
1 bond
none
To determine a molecule’s formula, use the atoms valences & the cross over rule
Ex. Water – why H2O?
Molecular Formulas:
Family 1 Family 6Valence 1 Valence 2
Makes 2 bondsMakes 1 bond
1 2
12
So, each H needs & makes 1
bond with O
So, the O needs & makes 2 bonds – 1
with each H
Cross Over Rules:
Write symbols for the elements, with the metal first
Write the valence of each atom
Cross over valences
If needed, simplify the valences
Eliminate any “1”s
2 1
Not needed here
Write symbols for the elements, with the metal first
Write the valence of each atom
Cross over valences
If needed, simplify the valences
Eliminate any “1”s
1 1
Not needed here
What is the molecular formula when Li & Br combine?
Write symbols for the elements, with the metal first
Write the valence of each atom
Cross over valences
If needed, simplify the valences
Eliminate any “1”s
2 1
Not needed here
What is the molecular formula when Be & Cl combine?
Write symbols for the elements, with the metal first
Write the valence of each atom
Cross over valences
If needed, simplify the valences
Eliminate any “1”s
3 2
Not needed
What is the molecular formula when Al & O combine?
Write symbols for the elements, with the metal first
Write the valence of each atom
Cross over valences
If needed, simplify the valences
Eliminate any “1”s
2 2
Both “2”s cancel each other out
11
What is the molecular formula when Mg & O combine?
Write symbols for the elements, with the metal first
Write the valence of each atom
Cross over valences
If needed, simplify the valences
Eliminate any “1”s
2 2
Both “2”s cancel each other out
11
What is the molecular formula when Ca & S combine?
Atom “X” from family II combines with atom “Y” from family VII. What is the compound’s molecular formula?
Atoms in Family Valence
1 1
2 2
3 3
4 4
5 3
6 2
7 1
2 1
Given the compound,
BxOyWhat would be the numerical value of “x” & “y”? Why?
B is from family 3, so it forms 3 bonds
O is from family 6, so it forms 2 bonds
Apply cross-over rule, x = 2 & y = 3
B2O3
Naming Molecules:
Scientists need a standardized way to name molecules.
Two methods:1. For molecules with a metal
& a non-metal
2. For molecules with 2 non-metals
Naming Molecules:
Steps to naming molecules with a metal & non-metal:
Identify the metal & the non-metal
metal non-metal
Name the metalsodium
Name the non-metal but change ending to “ide”
chloride
Name Al2O3
Identify the metal & the non-metal
metal non-metal
Name the metalaluminum
Name the non-metal but change ending to “ide”
oxide
Name CaF2
Identify the metal & the non-metal
metal non-metal
Name the metalcalcium
Name the non-metal but change ending to “ide”
fluoride
Naming Molecules:Steps to naming molecules with a 2 non-metals:
Name the first non-metal
Name the second non-metal, change ending to “ide”
carbon
Add prefixes to each non-metal
oxide
# of Atoms
Prefix
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
mono di
“mono” never placed on 1st non-metal!!!
Steps to naming molecules with a 2 non-metals:
Name the first non-metal
Name the second non-metal, change ending to “ide”
phosphorus
Add prefixes to each non-metal
oxide
# of Atoms
Prefix
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
di penta
Name P2O5
Steps to naming molecules with a 2 non-metals:
Name the first non-metal
Name the second non-metal, change ending to “ide”
carbon
Add prefixes to each non-metal
bromide
# of Atoms
Prefix
1 mono
2 di
3 tri
4 tetra
5 penta
6 hexa
tetra
Name CBr4
Name the following compounds:
a) CF4
b) MgCl2
c) Na2O
d) N2S3
carbon tetrafluoride
magnesium chloride
sodium oxide
dinitrogen trisulfide
Elements combine to form molecules in specific ratio to become stable (fill outer electron shell) Octet Rule
Use Cross Over Rule & Valences to determine a molecule’s formula
Atoms in Family Valence
1 1
2 2
3 3
4 4
5 3
6 2
7 1
Naming compounds with a metal & non-metal:
name of metal + name of non-metal – ide
Naming compounds with 2 non-metals:
prefix-name of non-metal + prefix-name of non-metal – ide
Activities:
436 Worksheet #3