Chemistry: Atom and Electrons Valence Electrons Essay

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Chemistry notes – 2013 – text book chapter 6
Periodic table: A table of the chemical elements arranged in order of atomic number.
Element: chemically the simplest substances that cannot be further simplified. Atoms of the substance all have the same number of protons.
Compound: a substance formed when two or more chemical elements are chemically bonded together
Atom: The basic unit of a chemical element. Containing protons, neutrons and electrons.
Nucleus: The positively charged central core of an atom, containing most of its mass. Contains neutrons and protons.
Neutron: A subatomic particle of about the same mass as a proton but without an electric charge, present in atomic nuclei
Proton: A stable subatomic particle occurring in all atomic nuclei, with a positive electric charge equal in magnitude to that of an electron.
Electron shell: a grouping of electrons surrounding the nucleus of an atom
Electron: A stable subatomic particle with a charge of negative electricity equal in magnitude to that of a proton.
Valence shell: The outermost electron shell of an atom consisting of the valence electrons
Valence electrons: electrons held in the valence shell
Group: (column) elements in the same group have similar properties. Atomic number increases by 1 for each element as you go across a group.
Period: (row) Number of electron shells increases by 1 for each element as you go down a period
Atomic number: the number of protons in the nucleus of an atom
Mass number: The total number of protons and neutrons in a nucleus.
Atomic mass: the mass of an atom expressed in atomic mass units where the mass of a hydrogen atom= 1
Atomic symbol: chemical symbol is a 1- or 2-letter internationally agreed code for a chemical element
Isotope: An Isotope of an element has the same atomic number (proton number) but a different atomic mass (protons + neutrons). Eg. Carbon 1, 2 and 3
Ionisation: the formation of ions by separating atoms or molecules or radicals or by adding or subtracting electrons from atoms
Ions: An atom with an electric charge due to the loss or gain of one or more electrons
Ionic bonds: The bonds that are formed after ions interact
Ionic compounds: compounds held together by ionic bonds

Periodic table
Dmitri Mendeleev- first person to develop the periodic table in 1869
Uranium is the last naturally occurring element
Order of elements in the table is based on atomic weight
Navigating the Periodic table
Rows – periods –Number of electron shells increases by 1 for each element as you go down a period
Columns – groups – elements in the same group have similar properties. Atomic number increases by 1 for each element as you go across a group.

Two main types of elements: metals and non-metals.
Metals
Alkali metals
Far left column
Group tells us they all have 1 electron in outer shell
Properties: low melting point, soft, highly reactive
React violently with water producing hydrogen gas and an alkaline solution
Further down the group the elements are the most reactive

Alkaline earth metals
Second column, group 2
All have 2 electrons in valence shell
Properties: low melting point, soft, highly reactive but not as reactive as alkali metals
React violently with water producing hydrogen gas and an alkaline solution
Further down the group the elements are the most reactive
Transition metals
Large block (10 groups) from groups 3-12.
Properties: some are magnetic, all silvery except gold and copper, many form coloured compounds, many form more than one compound with a non-metal like chlorine eg FeCl2 and FeCl3
Metalloids
Small set of elements situated between metals and non-metals
‘staircase’
Exhibit properties of both a metal and non-metal
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