Chemistry C1

• All substances are made of atoms.
• Elements are made of only one type of atom.
• Chemical symbols are used to represent atoms.
• Compounds contain more than one element

There are about 100 different elements from which all substances are made

The elements in the periodic table are arranged in columns called groups and usually have similar properties.

Atoms consist of a small nucleus surrounded by electrons

• The nucleus of an atom is made of protons and neutrons.
• Protons have a Positive charge.
• Electrons have a negative charge.
• Neutrons are Not charged.
• The atomic number (or proton number) of an element is equal to the number of protons in the nucleus of its atoms.
• Elements are arranged in order of their atomic numbers in the periodic table.
• The mass number is the sum of the protons and neutrons in the nucleus of an atom.

understanding the structure of an atom gives us important clues to the way substances react together.

• The reactants of the unreactive noble gasses ( in group 0 ) all have very stable arrangments of electrons.
• Electrons on atoms are in energy levels that can be represented by shells.
• Electrons in the lowest energy level are in the shell closest to the nucleus.
• Electrons occupy the lowest energy levels first.
• All the elements in the same group of the periodic table have the same number of electrons on their highest energy level (outer shell).

• compounds of metals bonded to non metals are called ionic bonds.
• the formula of an ionic compound shows the simplest ratio of ions.
• compounds of non metals have covalent bonds.
• The formula of a molecule shows the number of atoms in the molecule.

When different elements combine they form compounds. this is an ionic bond

• Atoms get rearanged in chemical reactions.
• The mass of the products is equal to the mass of reactants.
• Symbol equations should always be balanced.

Atoms are neither created or destroyes in a chemical reaction.