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, H 2 O

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 Shells Each shell can hold up to a specific number of electrons. 1 st Energy Level-maximum 2 electrons 2 nd – maximum of 8 electrons It is the electrons in the outermost shell that determines 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. Polar Covalent 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.