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B.8-B.9 In which you will learn about: •Atomic number & mass number •Ions •Naming ionic compounds 8.5 The Electrical Nature of Matter An atom consists of a • nucleus – (of protons and neutrons) • electrons in space about the nucleus. Electron cloud Nucleus • An atom is the smallest particle of an element that has the chemical properties of the element. Copper atoms on silica surface. Distance across = 1.8 nanometer (1.8 x 10-9 m) Subatomic Particles • Quarks – component of protons & neutrons – 6 types – 3 quarks = 1 proton or 1 neutron He ATOM COMPOSITION The atom is mostly empty space •protons and neutrons in the nucleus. •the number of electrons is equal to the number of protons. •electrons in space around the nucleus. •extremely small. One teaspoon of water has 3 times as many atoms as the Atlantic Ocean has teaspoons of water. ATOMIC COMPOSITION • Protons (p+) – – – + electrical charge mass = 1.672623 x 10-24 g relative mass = 1.007 atomic mass units (amu) but we can round to 1 • Electrons (e-) – – negative electrical charge relative mass = 0.0005 amu but we can round to 0 • Neutrons (no) – no electrical charge – mass = 1.009 amu but we can round to 1 Atomic Number, Z All atoms of the same element have the same number of protons in the nucleus, Z 13 Al 26.981 Atomic number Atom symbol AVERAGE Atomic Mass Mass Number, A • C atom with 6 protons and 6 neutrons is the mass standard • = 12 atomic mass units • Mass Number (A) = # protons + # neutrons • NOT on the periodic table…(it is the AVERAGE atomic mass on the table) • A boron atom can have A = 5 p + 5 n = 10 amu A 10 Z 5 B Atomic Symbols Show the name of the element, a hyphen, and the mass number in hyphen notation sodium-23 Show the mass number and atomic number in nuclear symbol form mass number 23 Na atomic number 11 Counting Protons, Neutrons, and Electrons • Protons: Atomic Number (from periodic table) • Neutrons: Mass Number minus the number of protons (mass number is protons and neutrons because the mass of electrons is negligible) • Electrons: – If it’s an atom, the protons and electrons must be the SAME so that it is has a net charge of zero (equal numbers of + and -) – If it does NOT have an equal number of electrons, it is not an atom, it is an ION. For each negative charge, add an extra electron. For each positive charge, subtract an electron (Don’t add a proton!!! That changes the element!) Learning Check – Counting Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms. 12C 13C 14C 6 6 6 #p+ _______ _______ _______ #no _______ _______ _______ #e- _______ _______ _______ B.9 Ions and Ionic Compounds • IONS are atoms or groups of atoms with a positive or negative charge. • Taking away an electron from an atom gives a CATION with a positive charge • Adding an electron to an atom gives an ANION with a negative charge. • To tell the difference between an atom and an ion, look to see if there is a charge in the superscript! Examples: Na+ Ca+2 I- O-2 vs. Na Ca I O Forming Cations & Anions A CATION forms when an atom loses one or more electrons. Mg --> Mg2+ + 2 e- An ANION forms when an atom gains one or more electrons F + e- --> F- PREDICTING ION CHARGES In general • metals (Mg) lose electrons ---> cations • nonmetals (F) gain electrons ---> anions Learning Check – Counting State the number of protons, neutrons, and electrons in each of these ions. 39 K+ 16O -2 41Ca +2 19 8 20 #p+ ______ ______ _______ #no ______ ______ _______ #e- ______ ______ _______ Charges on Common Ions -3 +1 -2 -1 +2 By losing or gaining e-, atom has same number of e-’s as nearest Group 8A (noble gas) atom. Forms of Chemical Bonds Most bonds are somewhere in between ionic and covalent. • There are 3 forms bonding atoms: • Ionic—complete transfer of 1 or more electrons from one atom to another (one loses, the other gains) • Covalent—some valence electrons shared between atoms • Metallic – holds atoms of a metal together Common Names • A lot of chemicals have common names as well as the proper IUPAC name. • Chemicals that should always be named by common name and never named by the IUPAC method are: – H2O water, not dihydrogen monoxide – NH3 ammonia, not nitrogen trihydride COMPOUNDS FORMED FROM IONS CATION + ANION ---> COMPOUND Na+ + Cl- --> NaCl A neutral compound requires equal number of + and - charges. +1 Predicting Charges on Monatomic Ions KNOW THESE !!!! +2 -3 -2 -1 Cd+2 0 Properties of Ionic Compounds Forming NaCl from Na and Cl2 • A metal atom can transfer an electron to a nonmetal. • The resulting cation and anion are attracted to each other by electrostatic forces. IONIC COMPOUNDS NH4+ Cl- ammonium chloride, NH4Cl Some Ionic Compounds Ca2+ + 2 F- ---> CaF2 Mg2+ + N-3 ----> Mg3N2 magnesium nitride Sn4+ + O2- ----> SnO2 Tin (IV) oxide calcium fluoride Formulas of Ionic Compounds Formulas of ionic compounds are determined from the charges on the ions atoms Na + F ions – : F : NaF : sodium + fluorine Charge balance: Na+ sodium fluoride formula 1+ = 0 1- Monatomic Ions Writing a Formula Write the formula for the ionic compound that will form between Ba2+ and Cl. Solution: 1. Balance charge with + and – ions 2. Write the positive ion of metal first, and the negative ion Cl Cl Ba2+ 3. Write the number of ions needed as subscripts BaCl2 Learning Check Write the correct formula for the compounds containing the following ions: 1. Na+, S2a) NaS b) Na2S c) NaS2 2. Al3+, Cla) AlCl3 b) AlCl c) Al3Cl 3. Mg2+, N3a) MgN b) Mg2N3 c) Mg3N2 Naming Compounds Binary Ionic Compounds: • 1. Cation first, then anion • 2. Monatomic cation = name of the element • Ca2+ = calcium ion • 3. Monatomic anion = root + -ide • Cl = chloride • CaCl2 = calcium chloride Naming Binary Ionic Compounds Examples: NaCl sodium chloride ZnI2 zinc iodide Al2O3 aluminum oxide Learning Check Complete the names of the following binary compounds: Na3N sodium ________________ KBr potassium ________________ Al2O3 aluminum ________________ MgS _________________________ Transition Metals Elements that can have more than one possible charge MUST have a Roman Numeral to indicate the charge on the individual ion. 1+ or 2+ Cu+, Cu2+ 2+ or 3+ Fe2+, Fe3+ copper(I) ion iron(II) ion copper (II) ion iron(III) ion Names of Variable Ions These elements REQUIRE Roman Numerals because they can have more than one possible charge: anything except Group 1A, 2A, Ag, Zn, Cd, and Al (You should already know the charges on these!) Or another way to say it is: Transition metals and the metals in groups 4A and 5A (except Ag, Zn, Cd, and Al) require a Roman Numeral. FeCl3 CuCl SnF4 PbCl2 Fe2S3 (Fe3+) iron (III) chloride (Cu+ ) copper (I) chloride (Sn4+) tin (IV) fluoride (Pb2+) lead (II) chloride (Fe3+) iron (III) sulfide Examples of Older Names of Cations formed from Transition Metals (you do not have to memorize these) Learning Check Complete the names of the following binary compounds with variable metal ions: FeBr2 iron (_____) bromide CuCl copper (_____) chloride SnO2 ___(_____ ) ______________ Fe2O3 ________________________ Hg2S ________________________ Polyatomic Ions NO3nitrate ion NO2nitrite ion Polyatomic Ions You can make additional polyatomic ions by adding a H+ to the ion! CO3 -2 is carbonate HCO3– is hydrogen carbonate H2PO4– is dihydrogen phosphate HSO4– is hydrogen sulfate Ternary Ionic Nomenclature Writing Formulas • Write each ion, cation first. Don’t show charges in the final formula. • Overall charge must equal zero. – If charges cancel, just write symbols. – If not, use subscripts to balance charges. • Use parentheses to show more than one of a particular polyatomic ion. • Use Roman numerals indicate the ion’s charge when needed (stock system) Naming Ternary Compounds Contains at least 3 elements There MUST be at least one polyatomic ion (it helps to circle the ions) Examples: NaNO3 Sodium nitrate K2SO4 Potassium sulfate Al(HCO3)3 Aluminum bicarbonate or Aluminum hydrogen carbonate Ternary Ionic Nomenclature Sodium Sulfate Na+ and SO4 -2 Na2SO4 Iron (III) hydroxide Fe+3 and OHFe(OH)3 Ammonium carbonate NH4+ and CO3 –2 (NH4)2CO3 Learning Check 1. aluminum nitrate a) AlNO3 b) Al(NO)3 c) Al(NO3)3 2. copper(II) nitrate a) CuNO3 b) Cu(NO3)2 c) Cu2(NO3) 3. Iron (III) hydroxide a) FeOH b) Fe3OH c) Fe(OH)3 4. Tin(IV) hydroxide a) Sn(OH)4 b) Sn(OH)2 c) Sn4(OH) Learning Check Match each set with the correct name: 1. Na2CO3 a) magnesium sulfite MgSO3 b) magnesium sulfate MgSO4 c) sodium carbonate 2. Ca(HCO3)2 a) calcium carbonate CaCO3 b) calcium phosphate Ca3(PO4)2 c) calcium bicarbonate Mixed Practice! Name the following: 1. Na2O 2. CaCO3 3. PbS2 4. Sn3N2 5. Cu3PO4 6. HgF2 Mixed Up… The Other Way Write the formula: 1. Copper (II) chlorate 2. Calcium nitride 3. Aluminum carbonate 4. Potassium bromide 5. Barium fluoride 6. Cesium hydroxide