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UNIT VIII ATOMS AND THE PERIODIC TABLE LESSON#1 ATOMIC NUMBER, ATOMIC MASS, ISOTOPES REVIEW VIII.1 THE STRUCTURE OF THE ATOM Some vocabulary: PROTONS: (P+) Positively charged subatomic particles that are found in the nucleus. NEUTRONS: (N) Neutrally charged subatomic particles that are ALSO found in the nucleus. * Elements are differentiated from one another by the number of protons in the nucleus. ****Different number of protons….different element.*** VIII.1 THE STRUCTURE OF THE ATOM (e-) Negatively charged subatomic particles that are found in orbitals around the nucleus. ELECTRONS: ***like satellites orbiting the earth*** ATOMIC NUMBER: Is the number found in the topic left hand corner of the element on the periodic table. Atomic # is equal to the number of protons an element has. What the periodic table tells you… 11 Na Sodium 22.99 Atomic Mass: The Atomic Number is equal to the # of protons (P+) in an element. *** Notice Atomic Mass is never a whole number….the extra little bit is from???? Electrons! Atomic Mass is equal to the # of protons plus the number of neutrons. P+ + N = Atomic Mass Atoms vs Ions Atoms are neutrally charged Ions are either positively or negatively charged. Atoms have equal number of protons and electrons. Ions have different numbers of protons and electrons. These inequalities determine the ions charge. 2 Protons 4 Electrons = -2 Charge VIII.1 THE STRUCTURE OF THE ATOM IONS: When electrons are added or taken away from an atom, an ion is formed (charged element). Atoms = Neutral…aka #P+ = #e- Ex: If an extra Chlorine atom: # protons: 17 Ions = Charged…aka #P+ ≠ #e- electron is added to a neutral # electrons: 17 + 1 Extra electron = 18 e- Charge on nucleus (Protons): +17 Charge of Electrons: -18 Total Charge of Atom: -1 VIII.1 THE STRUCTURE OF THE ATOM 11 17 17 11 11P+ + 10e- = +1 17P+ + 18e- = -1 VIII.1 THE STRUCTURE OF THE ATOM VIII.1 THE STRUCTURE OF THE ATOM Ex: If 2 electrons (e-) are removed from Barium (Ba) # protons: 56 # electrons: 56 – 2 = 54 Charge on nucleus (Protons): +56 Charge of Electrons: -54 Total Charge of Atom: +2 VIII.1 THE STRUCTURE OF THE ATOM Ex: How many electrons are possessed by Ca2+? Find Ca on the periodic table Ca’s atomic number is 20. 20 -2 = 18 protons So 20 – 2 less electrons because it 2+ How many protons are in Ca+2 ? 20 VIII.1 THE STRUCTURE OF THE ATOM Atomic mass: Equal to the number of protons to neutrons….mostly*** Formula: Atomic Number: # P+ + N = Atomic Mass = Number of Protons Therefore: N = Atomic Mass - # P+ THE STRUCTURE OF THE ATOM Practice Questions Ex: Find the number of protons, neutrons and electrons possessed by the following atoms: 12 6 C Atomic number Protons: 6 Electrons: 6 Neutrons: 6 Atomic Mass # P+ + N = Atomic Mass So N = Atomic Mass - # P+ N = 12 – 6 N=6 THE STRUCTURE OF THE ATOM Practice Questions Ex: Find the number of protons, neutrons and electrons possessed by the following atoms: 65 Zn3+ Protons: 30 30 Electrons: 30 -3 = 27 Neutrons: 65-30 = 35 VIII.1 THE STRUCTURE OF THE ATOM Isotopes: Atoms with same # of protons, but different # of neutrons; therefore different atomic mass! If you add a proton to an atom, a new element is produced: 12 Carbon + 6 proton (P+) → 12 Nitrogen 7 If you add a neutron to an atom, you get the same element but heavier; in other words an isotope! 12 6 C + n → 13 C 6 VIII.1 THE STRUCTURE OF THE ATOM Three Hydrogen-isotopes: 1. H = H = Hydrogen 2. H = D = Deuterium 3. H = T = Tritium C-isotopes: VIII.1 THE STRUCTURE OF THE ATOM E. Natural Mixtures of Isotopes Molar Mass --- is really an average value for a MIXTURE ALL POSSIBLE isotopes. VIII.1 THE STRUCTURE OF THE ATOM Ex: The following mixtures of isotopes are found in nature – calculate the expected molar mass for the following elements with from their isotopes. a) Ga-69 = 60.0% , Ga-71 = 40.0% **To get the average molar mass multiply the percentage (In decimal form) by the molar mass for each isotope and add them together.** Ga-69 = 0.60 X 69g/mol = 41.4 g/mol Ga-71 = 0.40 X 71g/mol = 28.4 g/mol Add = 69.8 g/mol VIII.1 THE STRUCTURE OF THE ATOM b) Ag-107 = 51.8%, Ag-109 = 48.2% Ag-107 = 0.518 X 107g/mol = 55.43 g/mol Add Ag-109 = 0.482 X 109g/mol = 52.54 g/mol = 107.9 g/mol Homework Hebden p.142-150) P. 142 # 2 P. 144 # 9, 10 P. 146 # 13 (a,c), 14 (a,c), 15 (a,c,e,h, i) P. 147 # 19 P. 150 # 23 (a,c,e,g)