What you should learn: How compounds differ from the elements that make them How a chemical formula represent the ratio of atoms in a compound How the same atoms can form different compounds

2.1 Elements combine to form compounds Compounds have different properties from the elements that make them Compound is a substance made of atoms of two or more different elements. Atoms of different elements are held together in compounds by chemical bonds Properties of the compound depend on which atoms the compound contains and how the atoms are arranged

2.1 Elements combine to form compounds Atoms combine in predictable numbers A compound always contains atoms of elements in a specific ratio Chemical formula uses chemical symbols to represent the atoms of the elements and their ratios in a chemical compound Subscripts, the small number written to the right of a chemical symbol, indicate the number of atoms that combine to make that compound

2.1 Elements combine to form compounds Same elements, Different Compounds Atoms of the same elements can form different compounds

Chapter 2.2 Chemical bonds hold compounds together What you should learn How electrons are involved in chemical bonding About the different types of chemical bonds How chemical bonds affect structure

Chapter 2.2 Chemical bonds hold compounds together Chemical bonds between atoms involve electrons Chemical bonds hold atoms together in compounds Chemical bonds form when electrons in the electron clouds around two atoms interact.

Chapter 2.2 Chemical bonds hold compounds together Atoms can transfer electrons. Gaining electrons changes an atom into negative ions. Losing electrons changes an atom into positive ions.

Chapter 2.2 Chemical bonds hold compounds together Ionic Bonds When ions are created, they are drawn toward one another by electrical attraction. This force of attraction between positive and negative ions is called an ionic bond. Electrical forces act in all directions; therefore each ion attracts all other nearby ions with opposite charges. These interactions make ionic compounds very stable and their crystals very strong.

Chapter 2.2 Chemical bonds hold compounds together Names of Ionic Compounds The name of an ionic compound is based on the names of the ions it is made of. The names for positive ions is the same as the name of the atom from which it is formed The name of a negative ion is formed by dropping the last part of the name and adding – ide Example of ionic bond: Example of naming ionic bonds:

Chapter 2.2 Chemical bonds hold compounds together Covalent Bonds Covalent bonds are when there are a pair of shared electrons between two atoms. Electrons are not gained or lost, The number of covalent bonds that form depends on the number of electrons that it has available for sharing. A group of atoms held together by covalent bonds is called a molecule.

Chapter 2.2 Chemical bonds hold compounds together Polar Covalent bonds When electrons of one element have a stronger attraction to one nucleus than to the other it will spend more time near that nucleus. When electrons are shared unequally, they are called polar covalent bonds.

Chapter 2.2 Chemical bonds hold compounds together Ionic compounds Most ionic compounds have a regular crystal structure. Covalent compounds Covalent compounds exist as individual molecules. Covalent compounds have a specific, three- dimensional shape called its molecular structure. Molecular shape can affect many properties of compounds.

Chapter 2.3 Substances’ properties depend on their bonds. What you should learn: How metal atoms form chemical bonds with one another. How ionic and covalent bonds influence substances’ properties.

Chapter 2.3 Substances’ properties depend on their bonds. Metals have unique bonds Metal atoms bond together by sharing their electrons with one another. The electrons are shared equally in all directions Metallic bond give metals distinct characteristics.

Chapter 2.3 Substances’ properties depend on their bonds. Ionic and covalent bonds give compounds certain properties. A compound’s properties depend on the chemical bonds that hold its atoms together. Covalent bonds have almost the opposite characteristics of ionic bonds.

Chapter 2.3 Substances’ properties depend on their bonds Bonds can make the same element look different. Covalent bonds do not always form small individual molecules.