The modern periodic table

The modern periodic table arranges elements by atomic number. Hydrogen (atomic number 1), because of its many unique properties, is placed at the top of the table in a cell by itself. Helium (atomic number 2) is placed at the top of the right-hand column above the other noble gases. Hydrogen and helium form the first series or period row).

The Element name and symbol are given for each element on P.T. The number at the top of each cell represents the atomic number of the element. The atomic number is the number of protons.

mass number = # of protons + # of neutrons The number at the bottom represents the average atomic mass of all the types of atoms of that element (isotopes). Atomic mass (atomic weight) - The average mass of atoms of an element, calculated using the relative abundance of isotopes in a naturally-occurring element. mass number = # of protons + # of neutrons

Periods- Each of the rows is considered to be a different period In the periodic table, elements have something in common if they are in the same row. All of the elements in a period have the same number of atomic orbitals. Every element in the top row (the first period) has one orbital for its electrons. All of the elements in the second row (the second period) have two orbitals for their electrons. It goes down the periodic table like that. At this time, the maximum number of electron orbitals or electron shells for any element is seven.

Groups The vertical columns are known as groups or families. There are 18 groups going from left to right. The elements are grouped together by their chemical properties. The chemical properties are based on their electron configuration. Every element in a group will have the same # of Valence electrons.

More about groups The first column (group) is called the alkali metals. The second column (group) is called the alkali earth metals. Groups 3-11 are the transition elements. Their common characteristics include: They are all metals Most have more than one oxidation state (possible valence electrons) Most form colored ions The 7th column is Halogens. The noble gases have 8 valence electrons (except helium (2 valence electrons for a full shell) and tend not to react with other elements.

Electrons The elements with 1 (alkali metals) or 2 valance electrons (alkali earth metals) are metals. They are unstable and will form cations (positive ions) by losing those electrons to reach the stable state of the noble gases. Elements with 7 valance electrons (halogens) are nonmetals will form anions (negative ions) by gaining electrons to become stable.

Electrons are the part of the atom that reacts with other atoms Electron configurations explain the recurrence of physical and chemical properties. If the outer shell has 4 or less electrons, the element will give up electrons in a chemical reaction. If the outer shell has more than 4 electrons, the element usually accepts electrons during a reaction.

General principles An atom has the same number of protons as it does electrons to be neutral. The electrons exists outside the nucleus in orbitals (levels of energy). The outer electrons, those involved in chemical reactions, are known as the valence electrons. Reactivity increases from top to bottom in a group of metals but decreases from top to bottom in the nonmetals.

Metals, non metals, metalloids

Metals, non metals, metalloids A metal is an element that readily loses electrons to form positive ions (cations) and has metallic bonds between metal atoms metals tend to be lustrous, ductile, malleable, and good conductors of electricity

Non-metals are most of the elements in groups 14-16 of the periodic table. Non-metals are not able to conduct electricity or heat very well. Unlike metals, non-metallic elements are very brittle, and cannot be rolled into wires or pounded into sheets. The non-metals exist in two of the three states of matter at room temperature: gases (such as oxygen) and solids (such as carbon). The non-metals have no metallic luster, and do not reflect light. They have oxidation numbers of ±4, -3, and -2.

Metalloids are the elements found along the stair-step line that distinguishes metals from non-metals Metalloids have properties of both metals and non-metals. Some of the metalloids, such as silicon and germanium, are semi-conductors. This means that they can carry an electrical charge under special conditions. They can be shiny or dull and their shape is easily changed. Metalloids typically conduct heat and electricity better than nonmetals but not as well as metals.