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Atomic Theory and the Periodic Table Atomic Theory All matter is made up of tiny particles called atoms An atom is the smallest part of an element that has all the element’s properties Atoms are not the smallest particles of matter Subatomic particles combine together to form atoms Protons Electrons Neutrons Protons have a charge of +1 Electrons have a charge of -1 Neutrons have a charge of 0 (neutral) The mass of protons and neutrons is almost 2000 times greater than the mass of an electrons Protons and neutrons form the core of an atom, called the nucleus The number of protons and neutrons add together to give the mass of the atom – each is designated a mass of 1 amu An atom isthe smallest the partnucleus of an are element Surrounding a series cloud like energy levelsproperties called shells that of has all the element’s or orbitals These shells are occupied by electrons Electrons are very light (approx. 0 amu) The electron cloud is 10,000 times larger than the nucleus Imagine the nucleus to be the size of a golf ball. Then on this scale the first electron shell would be about one kilometer from the golf ball, the second shell about four kilometers, the third nine kilometers etc. Electrons surround the nucleus in shells Each shell has a specific energy level The innermost shell holds 2 electrons The next two shells holds 8 electrons The outermost shell is called the valence shell The electrons in the valence shell are called valence electrons When the number of electrons equals the number of protons, the atom is neutral (no charge) When there are more electrons (-) than protons (+) the charge is negative When there are less electrons (-) than protons (+) the charge is positive Ions A Bohr-Rutherford diagram of an atom shows the arrangement and number of electrons in each shell. N 7p 7n S Cl 16p 16n 17p 18n Let’s look at an example… Sulphur atomic number 16 S sulphur 32.07 Atomic Number: ion charge = # of protons = # of electrons 2(in neutral atom) = 16 Atomic Mass: = # of protons + # of neutrons 32 = 16 + # of neutrons atomic mass # of neutrons = 16 Sulphur Bohr-Rutherford Diagram: S 32.07 16 p 16 n Electrons pair up if more than 4 2- sulphur Remember: the first shell holds 2 e’s, the next two shells hold 8 e’s each Electrons drawn as far apart as possible 16 Sulphur Bohr Diagram: first shell: 2 electrons second shell: 8 electrons Atomic number = 16 16 p 16 n third shell: 6 electrons total: 16 electrons In a sulphur atom, the valence shell has 6 electrons The Periodic Table of Elements Periodic Table The Periodic Table Elements are arranged in increasing order of atomic number The atomic number tells the number of protons in the atom. The horizontal rows of the periodic table are called periods The vertical columns are called families or groups Elements in the same family have similar chemical and physical properties Periodic Table Metals Metals are on the left and in the centre of the periodic table Metals have the following properties: Conduct heat and electricity Malleable and ductile Shiny, most are silver Solid at room temperature (except mercury) Metals Non-Metals Non-Metals are on the right side of the periodic table Non-Metals have the following properties: Poor conductors of heat and electricity Usually solid or gas at room temperature (only Bromine is a liquid) Brittle Dull Non-Metals Metalloids Metals are separated from non-metals by a staircase of elements called metalloids Metalloids have a blend of properties between metals and non-metals Tellurium Silicon Metalloids Chemical Families Chemical Families Alkali Metals (Group 1) soft, silver-grey metals Reacts easily with water Alkaline Earth Metals (Group 2) silver-grey metals harder and less reactive than group 1 metals Chemical Families Halogens (Group 17) coloured non-metals very reactive Noble Gases (Group 18) Colourless non-metals odourless very unreactive (does not combine easily with other atoms) Chemical Families • All elements in the same family (or group) have the same number of valence electrons Alkali Metals have 1 valence electron