Chemistry Unit 1 Chapter 1

Chapter 1

All elements are made up of atoms. When two or more atoms join together a molecule is formed. The atoms in elements and compounds are held tightly to each other by chemical bonds.

In the nucleus of atoms there are protons and neutrons. Around the nucleus there are electrons which have a negative charge. In the periodic table, atoms are arranged in order of their atomic number.

The electrons in an atom are arranged the nucleus in shells (energy levels). The electrons further away from the nucleus have more energy than those close to the nucleus. All elements in the same group of the periodic table have the same number of electrons in their outermost shell.

Metal atoms form positively charged ions because they lose one or more electrons when they combine with non-metals. Non-metal atoms gain electrons in the reaction, forming negative ions. The oppositely charged ions attract each other. This is called ionic bonding. When non-metals combine with each other, they form covalent bonds. Their atoms share electrons.

It is important that all symbol equations are balanced because atoms cannot be created nor destroyed in a chemical re

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