Intro to Chemistry What are the molecules on the left of the - - PDF document

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Intro to Chemistry

Central Questions

• Where can you find the chemical symbols for the

different elements?

• What are the molecules on the left of the equation

called? What about on the right?

Atoms

• All particles of matter are made of atoms.
• Atoms are made of:
• Protons +
• Neutrons-neutral
• Electrons –
• Protons and electrons are the same number unless it has a charge
• Element: pure substance of only one kind of atom (ex. Gold). 118 are

found on the periodic table.

• Atomic Number: # of protons
• Atomic Mass: protons + neutrons

Element Example 8 O Oxygen 15.999

Atomic # Atomic Mass What is the number of protons? What is the number of neutrons? What is the number of electrons?

Bond Types

• Compound—substance made of 2 or more atoms

joined together by a chemical bond

• Covalent bond—share electrons, strongest
• Ionic bonds—electrons are gained or lost; break

down in water (salt)

• Hydrogen bonds—attraction between partial

positive and partial negative charges; common in water

Chemical Formula

• Chemical formulas show the elements and

number of atoms of each element in a molecule

• H2SO4

Subscript Elements Hydrogen: 2 atoms Sulfur: 1 atom Oxygen: 4 atoms 7 atoms total

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Coefficients

• A formula may begin with a number called a coefficient. It

represents the # of molecules of that compound or atom need in the reaction.

• For example:
• 2H2SO4—2 molecules of Sulfuric Acid

Coefficients

• 2H2SO4—2 molecules of Sulfuric Acid
• A coefficient is distributed to ALL elements in a

compound

• 2—H2 (for a total of 4 H atoms)
• 2—S (for a total of 2 S atoms)
• 2—O4 (for a total of 8 O atoms)

Reading Chemical Equations

• Each side of an equation represents a combination of

chemicals.

• The combination is written as a set of chemical

formulas, separated by + symbols. CH4 + 2O2  CO2 + 2H2O

Coefficient

Reading Chemical Equations

• The two sides of the equation are separated by an

arrow.

• The combination of chemicals before the reaction

are on the left side of the arrow. These are the reactants.

• The right side indicates the combination of

chemicals after the reaction. These are the products.

For Example:

REACTANTS PRODUCTS Na + O2  Na2O

• The reactants are Na and O2
• The products are Na2O

Balancing Equations

• The Law of Conservation of Mass states that in a

chemical reaction, the quantity or amount of each element does not change.

• This means that each side of the equation must

represent the same quantity of each element; in other words have the same number of each kind of atom.

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Balancing Equations

Na + O2  Na2O

• In order for this equation to be balanced, there

must be equal amount of Na on the left hand side and on the right hand side.

• Right now, there is 1 Na atom on the left but 2

Na atoms on the right. We solve this problem by putting a 2 in front of the Na on the left hand side, like this: 2Na + O2  Na2O

Balancing Equations

2Na + O2  Na2O

• There are 2 Na’s on the left and 2 Na’s on the right. But

what about the O?

• We now must check to see if the O’s are balanced on both

sides of the equation. On the left hand side, there are 2 O’s and the right hand side only has one. This is still an unbalanced equation. To fix this, we must put a 2 in front

• f the Na2O on the right hand side. Now our equation

reads: 2Na + O2  2Na2O Is this equation balanced now?

Central Questions

• Where can you find the chemical symbols for the

different elements?

• What are the molecules on the left of the equation

called? What about on the right?