The periodic Table and the atom Lesson 3

Elements and the Periodic Table Elements are pure substances that consist of atoms. The periodic table consists of over 100 elements all of which have a certain spot on the table.

The periodic table of elements

Important Features of the Table The elements are also organized in two fashions horizontal vertical and horizontal lines called groups and periods.   Groups- elements with similar chemical properties in a vertical column in the main part of the table; Period – elements, arranged in a horizontal row, whose properties change from metallic on the left to non-metallic on the right

Groups / families Periods

Metals- Left side of the periodic table The majority of elements on the periodic table are metals . All metals, except for mercury are solids at room temperature. Metals have the following properties. Malleable : The ability to be hammered or bent into a shape. Lustre : They are shiny in appearance. Ductile : They can be pulled into a wire. Conductor of electricity: Electricity can travel through the metal.

Non-Metals- Right side of the periodic table Most of the remaining elements in the periodic table are non-metals . Non-metals generally have these properties: Non-conductor of electricity in its solid form At room temperature most are gasses or solids . Solids are brittle and lack the lustre of metals

Metalloids- middle right of the periodic table Some elements do not fit as metals or non-metals. These fit on either side of the staircase that divides the metals and the non-metals. They have some properties of metals and some properties of non- metals.

Group Names Alkali Metals: This is the first group in the periodic table. They are soft , silver coloured, solids and at room temperature and react violently with water. They must be stored in oil to prevent them from reacting.

Group Names Alkaline earth metals: This is the second group in the periodic table. They are light, very reactive, solids at room temperature and all react with oxygen in the air.

Group Names Transition metals: Theses metals have a wide variety of properties and reactivates. They are generally hard , strong metals that conduct electricity

Group Names Representative elements: Groups 1,2 and 13-17. There are metals and non-metals. Some are solids while others are gases and there is one liquid . They follow the periodic law.

Group Names Halogens: Non-metals in group 17. They may be solids, liquids or gasses and are extremely reactive .

Group Names Noble gasses: They are gasses at room temperature. They have a low melting point and boiling point. They are also very un- reactive .

Elements and Atomic Structure Atoms are composed of three subatomic particles Protons- Heavy positively charged particle found in the nucleus Neutrons -are neutral particles that have the same mass as protons and are located in the nucleus Electrons- Negatively charged particles with almost no mass. They circle the nucleus at different energy levels. The nucleus contains the protons and neutrons

nucleus

Atomic Number (Z) Atomic number - the number of protons in an atom of an element. Each element has a set number of protons and every atom from that element will have that many protons. The pattern for increasing protons moves from left to right and then down to the next row just like reading a book.

Atomic Mass (A) Atomic mass - the average mass of an element’s atoms. Total mass of protons and neutrons. Atomic mass is given in atomic mass units (amu). H has a mass of 1.01 amu. This means that iron atoms are about 55.85 times heavier than hydrogen atoms. Atomic masses are always expressed as decimal fractions. One reason that they do not have whole number values is that, except for fluorine, atoms of the same element have different numbers of neutrons.

Atomic Mass (A) Example: A hydrogen atom has one proton and one electron but no neutron. A small percentage of hydrogen atoms have 1 p, 1e, and 1n. 1 p, 1e, and 2n. Atomic mass generally increases in order of atomic number. Exception: iodine (I) has a lower atomic mass than tellurium (Te).

Example: Oxygen has an atomic number of 8 and a atomic mass of 16.00 N = A – Z N = 16.00 – 8 = 8 neutrons Work on the worksheet