The Chemistry of Living Cells

What are ATOMS?•Atoms are the basic building blocks of matter that make up everyday objects. A desk, the air, even you are made up of atoms!

•There are 90 naturally occurring kinds of atoms. Scientists in labs have been able to make about 25 more.

Everything is composed of ATOMS!

Atoms are made of?• Three basic particles:

– Electrons-carry a negative charge, are outside nucleus (in a neutral atom, same # as # of protons)

– Protons-carry a positive charge, are inside nucleus

(in a neutral atom, same # as # of electrons)– Neutrons-carry NO charge, are inside nucleus

– Ions = atoms (or molecules)

with missing or extra electrons,

giving it an electrical charge

(+ or -)

Draw this diagram and label the parts:

Atoms Contain Energy!• It takes energy to prevent the (-) electrons from

crashing into the (+) protons. WHY?

• Electrons are organized in an electron cloud in different energy levels.

• The farther away from the nucleus the energy levels is, the higher the energy.

The electron cloud shows the most probable location of the electrons. More to come in Chemistry!!!

Energy Levels

• VALENCE ELECTRONS – The electrons in the outermost energy level. – The maximum number is 8. These are the electrons

involved in chemical bonding.

• The energy level can have less than the maximum but then it is UNSTABLE/UNHAPPY.

• The atom will GAIN or LOSE electrons to become stable add: (OR IT MAY SHARE!!!!)

This will get more complicated in chemistry!!!)

Periodic Table Represents atoms that make up elements

Elements• ELEMENTS: Pure substances that consist

entirely of one type of atom; Cannot be broken down into simpler substances

• Elements related to living things:

How to read an element on the periodic table?

Atomic # = # of protons and #electrons Atomic mass = # of protons PLUS # neutrons

Protons = atomic # Electrons = same as protons/atomic # Neutrons = atomic mass – atomic #

Practice!!

• Hydrogen • Carbon

Answers!

• Hydrogen• Atomic # = 1• Atomic mass = 1• Protons = 1• Electrons = 1• Neutrons = 0

• Carbon• Atomic # = 6• Atomic mass = 12• Protons = 6• Electrons = 6• Neutrons = 6

Extension: Draw these atoms above the chart!!!

Bonds and Compounds

• COMPOUND = a group of atoms held together by chemical bonds. Example: NaCl, H2O

Chemical Formulas for Compounds

• CHEMICAL FORMULA: Shows the number of each element in the compound

Each capital letter is a new element• Subscript: (# below the symbol) tells how

many atoms of that element there are– If there is not a subscript, it is considered ONE

atom

• Coefficient: # in front of the chemical formula, tells how many of that compound there are

Examples: C6H12O6 2C6H12O6

Types of Bonds

• Covalent

• Ionic

• Hydrogen

COVALENT BONDS = Occur when two atoms share a pair of electrons; called molecules, not compounds

MOLECULE = a group of atoms held together by covalent bonds.Example = Water

IONIC BONDS = when one or more electrons are transferred from one atom to another (one loses electron(s), one gains electron(s)

*Sodium loses an electron-becomes a positive cation.

*Chlorine gains an electron; becomes a negative anion.

The attraction between the cation and anion makes the ionic bond.

• HYDROGEN BOND = a weak chemical bond that forms between 2 polar molecules.

• POLAR MOLECULES = unequal areas of charge.

• Water molecules have a slight (+) charge at the hydrogen and slight (-) charge at the oxygen that causes them to attract forming hydrogen bonds.

Summary of chemical bonds

• Covalent: weak (melting sugar)

• Ionic: strong (hard to melt salt)

• Hydrogen bonds: weakest (individually), but strong collectively.