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simplest kind of matter Cannot be broken down into simpler All one kind of atom. There are 117 of these known to man Elements:

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Elements are symbolized by one or two letters.

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The First Twenty Elements AtomicNumberSymbolNameAtomicNumberSymbolName 1Hhydrogen11Nasodium 2Hehelium12Mgmagnesium 3Lilithium13Alaluminum 4Beberyllium14Sisilicon 5Bboron15Pphosphorus 6Ccarbon16Ssulphur 7Nnitrogen17Clchlorine 8Ooxygen18Arargon 9Ffluorine19Kpotassium 10Neneon20Cacalcium Click to move on

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Each element has a specific number of protons in its nucleus. The identity of an atom is determined by the number of protons in its nucleus = the atomic number. The atomic number of an element never changes. Example: Gold atoms have 79 protons so the atomic number of gold is 79!

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All atoms of the same element have the same number of protons: The atomic number (Z)

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The total # of protons and neutrons in an atoms nucleus = atomic mass number. The number of neutrons in an atom can change, even though the protons cannot. So, the atomic mass number can change. Isotopes are atoms of the same element that have a different number of neutrons.

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The mass of an atom in atomic mass units (amu) is the total number of protons and neutrons in the atom.

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Atomic and molecular masses can be measured with great accuracy with a mass spectrometer.

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Atoms of the same element with different masses. Isotopes have different numbers of neutrons. 11 6 C 12 6 C 13 6 C 14 6 C

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# protons = atomic number # protons + # neutrons = atomic mass number Example: CHLORINE Atomic number = 17 Atomic mass number = 25 or 27 Protons = 17 Neutrons = [25-17 = 8] or [27-17 = 10]

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Element Atomic # Atomic Mass # # of Protons # of Neutrons # of Electrons 24 Mg 12 39 K 19 23 Na 11 19 F 9 27 Al 13 2H2H112H2H111 52 Mn 25

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Know the number of protons, neutrons and electrons in the atom. Know the number of electrons that each electron shell will hold.

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ELECTRONIC CONFIGURATION With electronic configuration elements are represented numerically by the number of electrons in their shells and number of shells. For example; N Nitrogen 7 14 2 in 1 st shell 5 in 2 nd shell configuration = 2, 5 2 + 5 = 7

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ELECTRONIC CONFIGURATION Write the electronic configuration for the following elements; Ca O ClSi Na 20 40 11 23 8 17 16 35 14 28 B 11 5 a)b)c) d)e)f) 2,8,8,22,8,1 2,8,72,8,42,3 2,6

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Boron = 5 protons, neutrons and electrons Contains protons & neutrons Can hold 2 electrons Can hold 8 electrons Can hold 18 electrons Protons Electrons Neutrons

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Protons Electrons Neutrons

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Protons Electrons Neutrons

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Protons Electrons Neutrons