Chemistry Basics -Part Two

Covalent Bonds Can Be Nonpolar Or Polar… Remember that covalent bonds occur between atoms that share electrons. There are two types of covalent bonds: Nonpolar Polar

What’s the Difference? While Nonpolar Molecules Share The Electrons Equally, Polar Molecules Do Not… This results in one part of the molecule being slightly positive and another part being slightly negative.

Water Is A Polar Molecule The oxygen in water is slightly negative, and the two hydrogen atoms are slightly positive. (–) (+) O H H

Hydrogen bond (+) H H (–) O Hydrogen Bonds are weak bonds that form between slightly + and – molecules… Hydrogen Bonds Form BETWEEN Water Molecules, in our DNA, and in proteins… animation animation

Because of Hydrogen Bonds… Water is cohesive. Cohesion is the tendency of water molecules to stick together. Cohesion on the surface of water is called surface tension! Water is adhesive. Adhesion is the attraction between molecules of different substances.

The surface tension of water allows a water strider to walk on water…

Water is rarely found in its pure form… Water is often found mixed with other molecules and elements. There are two types of mixtures: Solutions Suspensions

A Solution Is A Homogeneous Mixture… In a solution the atoms or molecules of the different substances are equally distributed. Examples: salt water & KoolAid + – – – – – – – – – – Na + + Cl –

Solutions Are Composed Of Two Parts… Solutions are always composed to two parts, a solute and a solvent. The solute dissolves in the solvent. Water is called the universal solvent because so many things dissolve in it.

Suspensions are heterogeneous mixtures… In a suspension the atoms or molecules that are mixed together do not spread out equally. Examples: Pennies in a glass of water

pH Stands For Potential Hydrogen… Mixtures are important to living things – one thing you need to know about mixtures is that they always have a pH (potential Hydrogen). pH measures whether it is an ACID or BASE.

In Solution Water Breaks Into Two Halves… As water mixes with other atoms it breaks apart… (or ionizes) H 2 O OH - and H + OH - (hydroxide ions) H + (hydrogen ions)

Acids Have A Low pH & Bases Have A High pH When water mixes with a base a lot of OH - (hydroxide ions) are produced. Bases have a pH higher than 7 on the scale. When water mixes with an acid a lot of H + (hydrogen ions) are produced. Acids have a pH lower than 7.

The pH scale Basic solution Oven cleaner Acidic solution Neutral solution pH scale Lemon juice, gastric juice Grapefruit juice, soft drink Tomato juice Human urine Pure water Human blood Seawater Milk of magnesia Household ammonia Household bleach Increasingly ACIDIC (Higher concentration of H + ) NEUTRAL [H + ]=[OH – ] H+H+ H+H+ H+H+ OH – H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ H+H+ Increasingly BASIC (Lower concentration of H + ) OH – H+H Animation

Chemical Reactions Occur In All Living Things… Chemical reactions are reactions that change the composition of matter. The general form of a chemical reaction is: Reactants Products. The reactants are the starting material, and the products are the result.

Sodium & Chlorine Combine To Make Table Salt What are the reactants and products of this reaction? Sodium ChlorineSodium Chloride

Hydrogen & Oxygen Combine To Form Water What are the reactants and products of this reaction? 2 H 2 O2O2 2 H 2 O

Equations Are Always Balanced… Notice that the number of atoms on each side of the equation is equal. This is a balanced equation! 2 H 2 O2O2 2 H 2 O