MARIEL: 
Chemistry is a branch of science that deals with chemical elements and compounds, and how these things work together. It is the study of the materials (things) that make up our bodies and everything in the world around us. 

NICOLAS: 

Basic concepts

The basic unit of an element is called an atom. An atom is the smallest building block that you can cut an element into without the element breaking down (turning into a lighter element, for example through nuclear fission or radioactive decay). A chemical compound is a substance made up of two or more elements. In a compound, two or more atoms are joined together to form a molecule. The tiniest speck of dust or drop of liquid, that one can see is made up of many millions or billions of these molecules. Mixtures are substances where chemicals are mixed but not reacted. An example would be mixing sand and salt. This can be undone again to produce salt and sand separately. Chemical compounds are changed by a chemical reaction. An example would be heating sodium bicarbonate, common baking soda. It will make water, carbon dioxide, and sodium carbonate. This reaction cannot be undone.

JULIAN:

Mole

A mole is a very large amount of atoms (602,214,150,000,000,000,000,000 atoms). The atomic mass of an element can be used to see how much of the element makes a mole. For example, the atomic mass of copper is about 63.55. That means about 63.55 grams of copper metal has a mole of atoms. The atomic mass of chlorine is about 35.45. That means 35.45 grams of chlorine has a mole of atoms in it.

Moles can be used to see how many molecules are in chemical compounds, too. Copper(II) chloride is an example. CuCl₂is its chemical formula. There is one copper atom (63.55) and two chlorine atoms (35.45 · 2 = 70.90). Add all the molar masses of the elements together to get the molar mass of the chemical compound (63.55 + 70.90 = 134.45). That means in 134.45 grams of copper(II) chloride, there is one mole of copper(II) chloride molecules. This concept is used to calculate how much chemicals are needed in a chemical reaction if no reactants (chemicals that are reacted) should be left. If too much reactant is used, there will be some reactants left in the chemical reaction.

LUCILA:

Acids and bases

Acids and bases are common chemicals. Acids release H⁺ ions when in water, and bases release OH⁻ ions when in water. Acids can react with bases. The H⁺ ion is taken from the acid by the base. This makes water, H₂O. A salt is also made when an acid and a base react together. An example would be reacting hydrochloric acid (HCl) and sodium hydroxide(NaOH). Hydrochloric acid releases H⁺ and Cl^- ions in water. The base releases Na⁺ and OH^- ions. The H⁺ and the OH^-react to make water. There is a solution of sodium chloride (NaCl) left. Sodium chloride is a salt.