Unit 2 Ecological Biochemistry Unit 2A: Basic Chemistry

Atoms are the Basic Units of Matter Atoms are incredibly small. Placed side by side, 100 million atoms would make a row only about 1 centimeter long—about the width of your little finger!

What are Atoms made of? Atoms are made of particles called protons, neutrons, and electrons. Protons have a positive (+) charge Electrons have a negative (-) charge Neutrons are neutral (no charge) Atoms normally have equal numbers of electrons and protons, making them neutral

Elements Elements are pure substances made of only one type of atom Elements are listed in the periodic table of elements They are arranged in order of their atomic numbers An atom is the smallest unit of an element that has the properties of that element

Atomic Number and Mass Number The atomic number of an element is the number of protons (typically the same as the number of electrons) The mass number of an element is the number of protons plus the number of neutrons

Element Symbol Atomic Number Mass Number Number of Protons Numbers of Neutrons Number of Electrons   Helium He 2 4 Magnesium Mg 12 Zinc Zn 30 65 35 Bromine Br 80 45 Aluminum Al 13 14

Important Elements for Biology The five most abundant elements in living things are: Hydrogen – 10% Oxygen – 65% Nitrogen – 4% Carbon – 19% Phosphorus – 1% H H

Molecules, Compounds, and Chemical Formulas A molecule is made when 2 or more of any atom are joined together (Ex: O2, H2O) A compound is a substance formed by the combination of two or more different elements (Ex: H2O, C6H12O6) All compounds are molecules, but not all molecules are compounds Chemical Formula- written shorthand showing the composition of a compound

Chemical Formulas Coefficient: tells how many molecules of that substance (the large number BEFORE the formula) Subscript: goes with the element symbol preceding the number; tells how many atoms of that element within one molecule of the substance (small number WITHIN the formula).

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Example 2: 6CO2 What is the coefficient? _______ What is carbon’s subscript? ________ What is oxygen’s subscript? ________ How many molecules of this compound are represented by this formula? _________ How many atoms TOTAL are present in this molecule? ______

Chemical Bonds The atoms in compounds are held together by chemical bonds. Making bonds involves the electrons that surround each nucleus. The electrons that are available to form bonds are called valence electrons.

This type of drawing is called a Bohr model Valence Electrons The electrons of an atom are spread out in different layers around the nucleus to make an “electron cloud” These layers are called energy levels 2 electrons go in the first energy level 8 electrons can go in the second energy level and beyond (octet rule) This type of drawing is called a Bohr model

Valence Electrons (cont.) If there are not 8 electrons for the outer level, these empty spots are called vacancies and some electrons are thus unpaired The unpaired electrons in the outer layer are the valence electrons The valence electrons can pair with those from other atoms to “fill” the vacancy This creates a molecule

Bohr Model vs. Lewis Dot Structure Lewis Dot Structure: shows just the valence electrons in the outer energy level Bohr Model: shows all of the electrons in their energy levels

Reactive vs. Stable The reactivity of an atom is determined by the number of vacancies in its outer energy level If there are vacancies, the atom is reactive/unstable If there are no vacancies, the atom is nonreactive/stable If the vacancies are filled due to bonding, the molecule is stable

The main types of chemical bonds are 1. ionic bonds 2. covalent bonds There are other types of bonds and interactions but they are not as strong as these two types

1. Ionic Bonds An ionic bond is formed when one or more electrons are transferred from one atom to another. An atom that loses electrons becomes positively charged. An atom that gains electrons has a negative charge. These positively and negatively charged atoms are known as ions. These oppositely charged ions have a strong attraction for each other, forming an ionic bond.

2. Covalent Bonds When electrons are shared by atoms instead of transferred. The moving electrons travel about the nuclei of both atoms, forming a covalent bond.

A covalent bond can be a… Single Covalent Bond: atoms share 2 electrons (1 pair) Double Covalent Bond: atoms share 4 electrons (2 pairs) Triple Covalent Bond: atoms share 6 electrons (3 pairs)

HONC This is the number of bonds each of these can form! H O N C 1 2 3 4   Bonds between the most important biological atoms will be covalent The number of bonds each can make is important for the compounds that will be created using these atoms Hydrogen -can form 1 single bond Oxygen- can form 2 single bonds or one double bond Nitrogen- can form 3 single bonds or 1 double bond and 1 single bond Carbon- can form 4 single bonds or 2 double bonds, or 1 double bond and 2 single bonds (no quadruple bond!)

Structural formulas Show you the types of elements in the molecule the number of atoms of each element AND the arrangement of atoms and location of covalent bonds. Shows the two dimensional shape of the molecule.

Chemical Reactions Chemical Reactions: process that changes or transforms one set of chemicals into another set of chemicals. Involves changes to the chemical bonds that join atoms in compounds. Reactants: elements or compounds that enter into a chemical reaction Products: elements or compounds produced by a chemical reaction HINT: Reactants react to produce products! Bonds of the reactants are broken and new bonds form in the products

Chemical Equations What process is this equation for? Chemical Equation: a mathematical representation of a chemical reaction. It shows the numbers and types of compounds involved. 6O2 + C6H12O6  6CO2 + 6H2O + ___

Balancing Chemical Equations The Law of Conservation of Matter: matter (atoms and elements) in a chemical reaction cannot be created or destroyed. Only the arrangement of the atoms is changed, NOT the number or types. Therefore both sides of a chemical equation must be “balanced” (have the same number of atoms).

Are these equations balanced?   C + 2H2 --> CH4 Na2SO4 + CaCl2 --> CaSO4 + NaCl C2H6 + O2 --> CO2 + H2O 2Al2O3 --> 4Al + 3O2