Classifying Elements Each element has a name and a symbol. The symbol is an abbreviated, or shortened version, of the element’s name. It is used to represent the element in chemical formulas and equations. Aurum is the Latin name for gold.

The elements in the Periodic Table are arranged so that elements with similar properties are close together. Example: fluorine (F) and chlorine (Cl) are gases that react very easily with other elements, so they are close together in the table. The Periodic Table gets its name from the fact that the elements’ properties repeat themselves every few elements, or periodically.

The vertical columns of elements are called groups. Some groups have special names: Group 1:The alkali metals Group 2:The alkaline earth metals Group 17:The halogens Group 18: The noble gases – unreactive, so they almost never react with other elements to make compounds.

The Periodic Table Column = Group or Family 18 columns on the Periodic Table Row = Period 7 rows on the Periodic Table

The horizontal rows of elements are called periods. The table also shows which elements are metals, non-metals, and metalloids.

Metals All metals look shiny. Metals are also malleable, meaning that they can be bent, or beaten into different shapes without breaking. All metals except mercury are solids at room temperature because they generally have high melting and boiling points. All metals let heat and electricity pass through them easily, so they are good conductors of heat and electricity. Most metals are very hard (a few so soft you can cut them with a knife). Only a few metals are magnetic (ex. - iron).

Nonmetals At room temperature most nonmetals are gases, some are solids and one (bromine) is a liquid. This is because nonmetals have a wide range of melting and boiling points. Nonmetals are not good conductors of electricity or heat (with the exception of carbon, which conducts electricity as well as a metal). All nonmetals are nonmagnetic.

Metalloids A few elements, such as silicon, have some of the properties of metals and some of the properties of nonmetals. Since they are not clearly one or the other, they are called metalloids, or semimetals. They are used in making semiconductors – materials which can conduct some electricity better than an insulator can, but not as well as a metal. They are used in making electronic components and microchips.

Compounds A compound is a substance that is made up of different elements. The atoms of the elements are joined together by chemical bonds. Bonds are chemical connections between atoms.

Types of Bonds There are two basic types of bonds: The reason that bonds occur is that atoms “want” to have full outer electron shells. An atom gets a full outer shell by getting involved in one of the two types of bonds. Covalent Ionic

Covalent Bonds Sharing one of more electrons is one type of bonding called a covalent bond. Example: water is formed when atoms of hydrogen share their electrons with an oxygen atom. A molecule is the smallest unit of a compound that has all the properties of the compound.

Ionic Bonds Example: salt is formed when the sodium gives up its electron and the chlorine takes it. The second type of bonding is when some atoms give up electrons, or ionic bonding. An atom like this that has lost or gained an electron is called an ion.

We write a + next to the element’s symbol if its atom has lost an electron and a – if it gains an electron. For example: Na becomes Na+ because it has more positive charge than negative and Cl becomes Cl- Opposites attract! The protons in the nucleus “miss” the “missing” electron and they stay close to it forming the bond.

If two types of atoms bond together using either method, the result is a compound. In a chemical change, bonds are made or broken, which leads to a new substance, or substances being created. In a physical change, such as making a mixture or dissolving something, no bonds are affected.

Mixtures There are two types of mixtures: A mixture is a combination of things where there are no chemical changes or bonds. Heterogeneous: Homogeneous: Not mixed evenly Each component retains its own properties Examples: pizza, cereal and milk, rocks in the sand at the beach, banana splits Mixed evenly throughout Properties are often different from their components Examples: milk, kool-aid, blood, lotion, window cleaner, glue

A solution is an evenly mixed mixture (liquid), such as salt water. Mixtures can be separated by physical means.

An isotope is an atom that has the same number of protons as another atom, but has a different number of neutrons.

Atoms of an element can lose or gain electrons and still be the same element, but the atom is no longer neutral. If the number of electrons is less than the number of protons, the atom will have a positive charge. Atoms with more electrons have a negative charge. Atoms of the same element with a different number of electrons are called ions.