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4.1 Atomic Theory & Bonding ATOM: smallest particle of an element, has a neutral charge. PEN = proton(s) + electron(s) + neutron(s) ELEMENT: made up of 1 type of atom (eg.oxygen O) IONS: atoms with charges (eg. oxygen is O2-) MOLECULES: groups of covalently bonded atoms (eg. oxygen molecules are O2) COMPOUNDS: are made up of at least 2 atoms bonded together. Hydrogen and oxygen are atoms/elements H2O is a compound Numbers to Remember : Protons = Atomic Number Neutrons = Mass number – Atomic number (Mass # - proton #). Electrons in an atom = atomic number (also proton #) Electrons in an ion = atomic number – ion charge Structure of an Atom: Name Symbol Charg e Location Atomic Mass Proton p 1+ nucleus 1 AMU Neutron n 0 nucleus 1 AMU Electron e 1– area surrounding the nucleus 1/1836 (0) Families of the Periodic Table: Columns of elements are called groups, or families All elements in a family have… similar properties bond with other elements in similar ways have the same number of valence electrons Family names (on the periodic table!): Group 1 = alkali metals (1+, highly reactive) Group 2 = alkaline earth metals (2+, reactive) Group 17 = the halogens (1-, very reactive) Group 18 = noble gases (0, unreactive) Periods are horizontal rows on the periodic table. 1 Periodic Table of the Elements Periodic Table & Ion Formation: Where are the following? INCREASING REACTIVITY • Atomic Number • Period • Group/Family • Metals • Non-metals • Transition metals • Metalloids • Alkali metals • Alkaline earth metals • Halogens Ions: Atoms that gain and lose electrons to become stable (full valence shells). 1. Cations: metals that lose electrons & form positive ions (Na+) Multivalent: Some metals can have more than one charge (Fe2+ or Fe3+). 2. Anions: Non-metals gain electrons & form negative ions (O-2) • Noble gases Bohr Diagrams: Bohr Diagrams Bohr diagrams show how many electrons appear in each electron shell around an atom. (2, 8, 8, 18, 18) Valence electrons: electrons in the outermost shell ONLY. If the valence shell is full = stable If the valence shell is not full = reactive What element is this? •It has 2 + 8 + 8 = 18 electrons, and therefore 18 protons 18 p 22 n •It has 8 electrons in the outer (valence) shell Argon! 2 Covalent Bonds: Ionic Bonds: Formed between cations (metal or NH4+) & anions (non-metal or polyatomic ions). Valence electrons are transferred to create the cation and anion. Eg. Li2O Formed between two or more non-metals Valence electrons are shared between atoms (so NO CHARGES are formed) Eg. HF + Lithium + Oxygen Electrons are transferred from the cations to the anion Li+ O2Li+ Lithium oxide, Li2O Lewis Diagrams: Lewis Diagrams for Ions: Ex. Nitrogen ion Remove or add electron dots to make full valence shells. Square brackets and the charge are placed around each ion Dots representing valence electrons are placed around the element symbols (on 4 sides, imagine a box around the symbol) Ex: Nitrogen atom Electrons are shared Fluorine Hydrogen Only valence electrons are shown Electron dots are placed singularly, then they are paired. Hydrogen fluoride •• • • • •• Be •• •• • • Cl • • •• Each beryllium has two electrons to transfer away, and each chlorine wants one more electron • • Cl •• •• •• • • • • Be • • •• • • Cl • • • • Since Be2+ wants to donate 2 electrons and each Cl– wants to accept only one, two Cl– ions are necessary • • •• – • • •• Cl 2+ •• • • • • •• Be • • – •• • Cl • •• The ionic compound Beryllium chloride is formed 3 Lewis Diagrams For Covalent Compounds: Lewis Diagrams for Ionic Compounds: •• • • • •• Be •• •• • • Cl • • •• Each beryllium has two electrons to transfer away, and each chlorine wants one more electron • • Cl •• • Be • • •• •• – •• •• • • • • • Cl • • • • Since Be2+ wants to donate 2 electrons and each Cl– wants to accept only one, two Cl– ions are necessary • • Cl •• •• 2+ •• • • • • •• Be • • – •• Cl • • •• The ionic compound Beryllium chloride is formed 4.2 – Ionic and Covalent Compound Naming Ionic Compounds: - are made up of positive and negative ions arranged in a crystal structure. Salt, NaCl Covalent Molecules: - are made up of atoms sharing electrons. valence electrons are drawn to show sharing of electrons. Remember: All atoms “like” to have a full valence shell The shared pairs (“bonding pairs”) of electrons are usually drawn as a straight line “lone pairs” are the electrons not shared Naming Ionic Compounds: name of an ionic compound = cation anion-ide Ex.1: magnesium and oxygen cation anion-ide Magnesium ox + ide Magnesium oxide Magnesium Ex.2: what is the name of Ca3N2? oxide is used as a drying agent. Ca = calcium; N = nitrogen Drop the end of the anion and add –ide Calcium nitride Ex.3: What is the name of BaCl2? Barium chloride Water, H2O 4 Writing formulas for Ionic Compounds Remember: positive charges must = negative charges Ex.1: What is the formula for magnesium phosphide? Magnesium is Mg2+ Phosphorous is P3– Lowest common multiple of 2 and 3 is 6 3 Mg2+ ions & 2 P3– ions (6 +ve’s & 6 –ve’s) Magnesium phosphide = Mg3P2 Ex.2: What is the formula for calcium oxide? Calcium is Ca2+ Oxygen is O2– 2+ 1 Ca ion & 1 O2– ion Calcium oxide = CaO Ionic Compound with a Multivalent Metal Multivalent: some transition metals have more than one charge. Roman numerals are used after the metal name to indicate which ion was used Ex. 1 What is the formula manganese(III) sulphide? This manganese is Mn3+ Sulphur is S2– Lowest common multiple of 3 and 2 is 6 2 Mn3+ ions and 3 S2– ions Mn2S3 Drawing Formula Diagrams Examples: Lithium nitride Barium sulphide You try! What is the name for TiF4? Titanium can be Ti4+ or Ti3+ Fluorine is F– From the ratio in the formula you can find out it is Ti4+ 1 Ti4+ ion and 4 F– ions Titanium (IV) fluoride 5 Polyatomic Ions are made up of several atoms joined together by covalent bonds The whole group has a + or – charge, not individual atoms. Ex.1 What is the formula of sodium sulphate? Ex.2: What is the name of the compound KClO? ClO– = hypochlorite K+ = potassium Potassium hypochlorite Ex.3: What is the formula for Calcium nitrate? and NO3Ca2+ Ca(NO3)2 Na+ and SO42– Na2SO4 Naming Simple Covalent Compounds Prefixes are used before the atom name to indicate the number of atoms in the molecule. * Note the brackets around NO3 show there are two of the nitrate ions present Examples: Examples: CO = carbon monoxide CO2 = carbon dioxide What is the name of the molecule Si3P6? Trisilicon hexaphosphide Write the most metallic atom (furthest left) first, then add -ide to the end of the second atom’s name What is the chemical formula for the molecule trinitrogen tetrachloride? N3Cl4 6 How do you know which type it is? To determine whether a compound is ionic or covalent: - Examine the formula • Ionic compounds start with a metal or the ammonium ion • Covalent compounds start with a non-metal 4.3 Chemical Equations A Chemical change means new compounds are formed. Law of Conservation of Mass: matter is not created or destroyed; atoms are just rearranged. mass of reactants = mass of products number of each = number of each atom in reactants atom in products If you could collect and measure all of the exhaust from this car, you would find that mass of reactants (gas + O2) = mass of products (exhaust)! Chemical reactions can be written in different ways. A word equation: Nitrogen monoxide + oxygen nitrogen dioxide A symbolic equation: State of matter 2NO(g) + O2(g) 2NO2(g) Writing and Balancing Chemical Equations word equation uses the names of the chemicals - Letters indicate the state of each compound Coefficients - indicate the ratio of compounds in the reaction - here, there is twice as much NO and NO2 than there is O2 (aq) =aqueous/ dissolved in water (s) = solid (l) = liquid Example: K + O2 K2O The word equation is: Potassium metal + oxygen gas potassium oxide (g) = gas 7 Tips and Tricks A skeleton equation shows only the formulas of the elements/compounds Shows atoms, but is not balanced K(s) + O2 (g) K2O(s) A balanced chemical equation shows the correct number of each atom Balancing ensures that the number of each atom is the same on both sides of the reaction arrow Always use the smallest whole number ratio 4K(s) + O2 (g) 2K2O(s) Use the chemical symbol to represent single elements. Be careful of diatomic and polyatomic elements such as O2, P4 and S8 The “special seven” are all diatomic elements (hockey stick & puck) H2, N2, O2, F2, Cl2, Br2, I2 Balancing Equations Examples Balance the following: __Sn(NO2)4 + __K3PO4 __KNO2 + __Sn3 (PO4)4 Balance the following: ___ C2H6 + ___ O2 ___ CO2 + ___ H2O 8