The Chemistry of Life

The Nature of Matter• Chemistry- The study of matter• Matter- Anything that takes up space and has

mass.• Mass- A measure of the amount of matter an

object contains.• Weight-measure of the gravitational pull on an

object.

Matter is made up of Elements

• Element- A substance that cannot be broken down into other substances by chemical reactions.

• There are 92 naturally occurring elements.• About 25 are essential to life.• 96% of living matter is made up of 4 elements

• What elements make up the remaining 4% of living Matter?

CHONPS • C- Carbon • H- Hydrogen • O- Oxygen • N- Nitrogen • P- Phosphorous • S- Sulfur

Elements Can Exist in Combinations

• Compound- A pure substance composed of 2 or more elements combined in a fixed ratio.

• Examples: NaCl,

H2O

What is an Atom? • Basic unit of matter• Smallest fragment • Incredibly Small• 100 million atoms would make a row of only 1

centimeter long ( width of little finger) • Atoms contains subatomic particles that are even

smaller

What are the Subatomic Particles in an Atom?

What are Elements? • Element- A pure substance that consists of

entirely of one type of atom• Represented by one or two letter symbols

• E.g. C, H, Na

• Periodic table of Elements

Protons and Neutrons • Same mass • Protons- Positively charged (+)• Neutrons- Carry No Charge (0)

• Neutral Particles

• Nucleus- Center of an Atom • Protons + Neutrons = Nucleus

Electron • Electron- Negatively charged particle (-)

• 1/1840 the mass of a proton• Constant motion in the space that surrounds the nucleus • Attracted to the positively charged nucleus • Remain outside of the nucleus

Atomic Number and Mass Number

• Atomic number- Number of protons and electrons in an atom of a particular element.

• Mass Number- Number of protons and neutrons in an atom.

• Can determine the number of neutrons by subtracting the atomic number from the mass number.

• Number of neutrons in an element can vary, number of protons is constant.

Example Carbon (C) • atomic number=6

• mass number=12

• number of electrons= _____• number of protons= _____• number of neutrons=___

Electron Arrangement Determines the Chemical

Properties of an Atom

• Potential Energy- Energy that matter stores because of its position or location.

• Electrons vary in their location in an atom;

• they exist at different energy levels or electron shells.

Electron ShellsEach shell can hold up to a specific number of

electrons.1st Energy Level-maximum 2 electrons2nd – maximum of 8 electronsIt is the electrons in theoutermost shell thatdetermines the chemical properties of an atom.

Valence Electrons • Valence electrons- Electrons in the outermost

energy shell.• Octet Rule= a valence shell is complete when it

contains 8 electrons ( except H and He).• Valence electrons are responsible for the atom’s

bonding ability.

Atoms combine by chemical bonding to form molecules• Atoms with incomplete valence shells tend to fill

those shells by reacting with other atoms.• Chemical bond= Attraction that holds molecules

together• Molecules= Two or more atoms held together by

chemical bonds.

Chemical Bonds• Ionic bonds are attractions between ions of

opposite charges.• Ion- an atom which has lost or gained an electron.• Example: NaCl

Covalent Bonds• Covalent bonds

occur when atoms share a pair of electrons.

• Example: water

Non-Polar vs. PolarCovalent Bonds

Electronegativity- An atom’s ability to attract and hold electrons.

• Non-polar covalent bonds are formed by an equal sharing of electrons.

• Polar covalent bonds are formed by an unequal sharing of electrons.

Hydrogen Bonds• Weak bond

formed between a positively charged hydrogen of one atom and the negatively charged region of another atom.

Chemical reactions make and break chemical bonds and

involve a change in energy!

•

Energy is Stored in Bonds

• Chemical reactions that release energy are exergonic (exothermic) reactions.

• Chemical reactions that store energy in bonds are endergonic (endothermic) reactions.