Download Chemical Formulas and Equations

Chemical Formulas and Equations
• Letters form words. In the same way,
chemical symbols are put together to
make chemical formulas that describe
substances. Chemical formulas can be
put together to make equations just like
words can be put together to make a
sentence.
Question 1
• What is a chemical formula?
Chemical Formula
• Shorthand way to use chemical symbols
and numbers to represent a substance.
• A chemical formula shows how many
atoms of each kind are present in a
molecule.
• NaCl
• H2O
• CO2
Question 2
• What is a subscript?
Subscript
• A number written below and to the
right of a chemical symbol in a
formula.
Subscript
• If there is no subscript, only one atom of
the element is present.
NaCl has one atom of sodium and one atom of chlorine.
Question 3
• What is a coefficient?
Coefficient?
• Numbers in front of the formulas.
Reactants

Products
Question 4
• How do you write the chemical formula for
a covalent compound?
Writing Formulas for Covalent Compounds
• Covalent compounds are composed of 2
nonmetals. Many covalent compounds use
prefixes that represents a number and tell how
many atoms of each element are in the formula.
Covalent Formulas
Carbon dioxide…The absence of a prefix indicates one
Carbon atom. The prefix di indicates two oxygen atoms.
Covalent Formulas
N2O
Dinitrogen monoxide…The prefix di indicates
two nitrogen atoms. The prefix mono indicates
One oxygen atom.
Question 5
• How do you write ionic compounds?
Ionic Compounds
Sodium Chloride…A sodium ion has a 1+ charge.
A chloride ion has a 1- charge. One sodium ion
and one chloride ion have an overall charge of 0.
Ionic Compounds
Magnesium chloride…A magnesium ion has a
2+ charge. A chloride ion has a 1- charge. One
Magnesium ion and two chloride ions have an
Overall charge of (2+) + 2(1-) = 0
Question 6
• What is a chemical equation?
Chemical Equation
• A shorthand description of a chemical reaction
using chemical formulas and symbols.
C + O2  CO2
Question 7
• What are reactants?
Reactants
• The starting materials in a chemical
reaction.
Question 8
• What are the products?
Products
• The substances formed in a chemical
reaction.
Question 9
• Where do the reactants appear in a
chemical reaction?
Chemical Reactions
• Reactants appear before the arrow and
products appear after the arrow.
Question 10
• What separates the formulas of the
reactants from the formulas of the
products?
Chemical Reactions
• The arrow (yields sign) separates the
reactants and products.
Yields sign
Question 11
• What separates the formulas?
Chemical Reactions
• A plus sign separates the formulas of two
or more reactants or products
C + CO2  CO2
Plus sign
Video
• Go to folder...click “chemical
equations…law of conservation of mass.”
The Importance of Accuracy
• CO2 is a colorless, odorless gas you exhale.
• CO is a colorless, odorless, and poisonous gas.
• Co is an element.
CO2
CO
Co
The Reason Equations Must be
Balanced
• Atoms are never lost or gained in a
chemical reaction...just rearranged. Every
atom in the reactant becomes part of the
products (balancing equations).
Balancing Equations
• Antoine Lavoisier (late 1700s) found the
total mass of reactants was always the
same as the total mass of the products.
Law of Conservation of mass
(Antoine Lavoisier)
Law of Conservation of Mass
• Mass is neither
created nor
destroyed in
ordinary chemical
and physical
changes.
Law of Conservation of Mass
• A chemical equation must show the same
numbers and kinds of atoms on both sides
of the arrow.
Question 12
• What is a coefficient?
To Balance an Equation
• You must use coefficients. A coefficient is
a number paced in front of a chemical
symbol.
Video
• Go to folder and click #2 “Balancing
Equations forming water”
To Balance an Equation
• How do you balance an equation?
To Balance an Equation
• All atoms must be counted. Multiply the
subscript of each element by the
coefficient.
• Count the atoms
• H2O
• 4CO2
• 2C6H12O6
• 4MgCl2
• 2Pb(NO3)2
To Balance an Equation
• Only coefficients, not subscripts are
changed when balancing equations.
Changing the subscripts will change the
compound.
To Balance an Equation
• Place coefficients in front of symbols that
are not balanced and repeat until all atoms
are the same in the reactants and
products.
Video
• Go to folder and click #3 “Balancing
Equations Forming Rust.”
Summary
• A chemical formula uses symbols and
subscripts to describe the makeup of a
compound.
Na2SO4
Summary
• Chemical formulas can often be written
from the names of covalent and ionic
compounds.
Covalent
ionic…AlCl3
Summary
• A chemical equation uses chemical
formulas, chemical symbols, and
coefficients to describe a reaction.
Summary
• Balancing an equation requires that the
same numbers and kinds of atoms be on
each side of the equation.
Summary
• A balanced equation illustrates the law of
conservation of mass: mass is neither
created nor destroyed during ordinary
physical and chemical changes.