4.1 Atomic Theory and Bonding

A Brief History of the Atom…

4.1 Atomic Theory and Bonding An atom is the smallest particle of an element that still has the properties of that element 50 million atoms, lined up end to end = 1 cm An atom = proton(s) + neutron(s) + electron(s) Atoms join together to form compounds. A compound is a pure substance that is composed of two or more atoms combined in a specific way. Oxygen and hydrogen are atoms/elements; H2O is a compound.

What are each of the following? Terms: Atom Molecule Compound Mixture

4.1 Atomic Theory and Bonding A chemical change occurs when the arrangement of atoms in compounds changes to form new compounds. **ACTIVITY**- Observing Chemical Changes pg 169 textbook -Not reversible -Ex. rusty nail, cooked eggs

4.1 Atomic Theory and Bonding Atoms are made up of smaller particles called subatomic particles.

4.1 Atomic Theory and Bonding The nucleus is at the centre of an atom. The nucleus is composed of protons and neutrons. Electrons exist in the space surrounding the nucleus. # of protons = # of electrons in every atom Nuclear charge = charge on the nucleus = # of protons Atomic number = # of protons = # of electrons

Review so far… Pg 171 textbook

Organization of the Periodic Table In the periodic table elements are listed in order by their atomic number. Metals are on the left (the transition metals range from group 3 to group 12), non-metals are on the right, and the metalloids form a “staircase” toward the right side.

Organization of the Periodic Table Rows of elements (across) are called periods. All elements in a period have their electrons in the same general area around their nucleus.

Organization of the Periodic Table Columns of elements are called groups, or families. All elements in a family have similar properties and bond with other elements in similar ways. Group 1 = alkali metals Group 2 = alkaline earth metals Group 17 = the halogens Group 18 = noble gases

Where are the following? INCREASING REACTIVITY Where are the following? Atomic number Period Group/Family Metals Non-metals Transition metals Metalloids Alkali metals Alkaline earth metals Halogens Noble gases See page 172

Periodic Table and Ion Formation Atoms gain and lose electrons to form bonds. The atoms become electrically charged particles called ions. Metals lose electrons and become positive ions (cations). See page 173

Periodic Table and Ion Formation Some metals (multivalent) lose electrons in different ways. For example, iron, Fe, loses either two (Fe2+) or three (Fe3+) electrons Neutral Atom Fe2+ Ion 26+ 26- 26+ 24- Fe3+ Ion 26+ 23-

Periodic Table and Ion Formation Non-metals gain electrons and become negative ions (anions). Atoms gain and lose electrons in an attempt to have the same number of valence electrons (electrons farthest from the nucleus) as the nearest noble gas in the periodic table.

To Do: Workbook Handouts- pg 60

Bohr Diagrams Bohr diagrams show how many electrons appear in each electron shell around an atom. Electrons in the outermost shell are called valence electrons. Think of the shells as being 3-D like spheres, not 2-D like circles.

What element is this? It has 2 + 8 + 8 = 18 electrons, and therefore, 18 protons. It has three electron shells, so it is in period 3. It has eight electrons in the outer (valence) shell. 18 p 22 n argon (c) McGraw Hill Ryerson 2007

Patterns of Electron Arrangement in Periods and Groups Electrons appear in shells in a very predictable manner. There is a maximum of two electrons in the first shell, eight in the 2nd shell, and eight in the 3rd shell. The period number = the number of shells in the atom. Except for the transition elements, the last digit of the group number = the number of electrons in the valence shell. The noble gas elements have full electron shells and are very stable. See page 175

Forming Compounds When two atoms get close together, their valence electrons interact. If the valence electrons can combine to form a low-energy bond, a compound is formed. Each atom in the compound attempts to have the stable number of valence electrons as the nearest noble gas. Metals may lose electrons and non-metals may gain electrons (ionic bond), or atoms may share electrons (covalent bond). See pages 176 - 177 (c) McGraw Hill Ryerson 2007

Forming Compounds Ionic bonds form when electrons are transferred from positive ions to negative ions. Covalent bonds form when electrons are shared between two non-metals. Electrons stay with their atom but overlap with other shells. (c) McGraw Hill Ryerson 2007

Forming Compounds (continued) Ionic bonds are formed between positive ions and negative ions. Generally, this is a metal (+) and a non-metal (-) ion. For example, lithium and oxygen form an ionic bond in the compound Li2O. + lithium oxygen Electrons are transferred from the positive ions to negative ions Li+ O2- Li+ lithium oxide, Li2O Lattice

Forming Compounds (continued) Covalent bonds are formed between two or more non-metals. Electrons are shared between atoms. + Hydrogen fluoride hydrogen fluorine electrons are shared (c) McGraw Hill Ryerson 2007

Lewis Diagrams Lewis diagrams illustrate chemical bonding by showing only an atom’s valence electrons and the chemical symbol. Dots representing electrons are placed around the element symbols at the points of the compass (north, east, south, and west). Electron dots are placed singly until the fifth electron is reached then they are paired. See page 178 (c) McGraw Hill Ryerson 2007

LEWIS DIAGRAMS FOR PERIODIC TABLE

Lewis Diagrams of Ions Lewis diagrams can be used to represent ions and ionic bonds. For positive ions, one electron dot is removed from the valence shell for each positive charge. For negative ions, one electron dot is added to each valence shell for each negative charge. Square brackets are placed around each ion to indicate transfer of electrons. (c) McGraw Hill Ryerson 2007

EXAMPLE OF IONIC BOND (MAKES IONS) – 2+ – • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • Be Cl Cl Be Cl Cl Be Cl Each beryllium has two electrons to transfer away, and each chlorine can receive one more electron. Since Be2+ can donate two electrons and each Cl– can accept only one, two Cl– ions are necessary. beryllium chloride See page 179

Lewis Diagrams of Covalent Bonds Lewis diagrams can also represent covalent bonds. Like Bohr diagrams, valence electrons are drawn to show sharing of electrons. The shared pairs of electrons are usually drawn as a straight line. EACH LINE IS TWO ELECTRONS See page 179 (c) McGraw Hill Ryerson 2007

EXAMPLE OF COVALENT BOND (SHARING ELECTRONS)

Lewis Diagrams of Diatomic Molecules Diatomic molecules, like O2, are also easy to draw as Lewis diagrams. • • • • • • • • • • • • • • • • • • • • • • • • O O O O O O Several non-metals join to form diatomic molecules. Valence electrons are shared, here in two pairs. This is drawn as a double bond. There are 7 diatomic molecules: -H2, O2, Br2, F2, I2, N2, Cl2 -They can be used to make the word _____________________ See page 180 (c) McGraw Hill Ryerson 2007

REVIEW Take the Section 4.1 Quiz

4.2 Names and Formulas of Compounds

4.2 Names and Formulas of Compounds Ionic compounds are made up of positive and negative ions. All of the positive and negative ions organize in a pattern. Negative-positive attract. Negative-negative and positive-positive repel. Ionic compounds form from the inside out as solid crystals. Ionic compounds are like a solid stack of bricks. Salt, NaCl A salt shaker contains thousands of small pieces of NaCl. See pages 184 - 185

4.2 Names and Formulas of Compounds Covalent molecules share electrons. There is generally no order to the formation of covalent molecules. These molecules clump together as solids, liquids or gases. Covalent molecules are like a play-pit full of plastic balls. Each plastic ball = 1 covalent molecule of H2O Water, H2O

The Chemical Name and Formula of an Ionic Compound Ionic compounds are composed of positive ions and negative ions. The name of an ionic compound = positive ion + negative ion-ide. For example, an ionic compound forms between magnesium and oxygen. The positive ion is the first part of the name, magnesium. The negative ion forms part of the ending of the name, oxygen. Add -ide to the end of the name to form magnesium oxide. Magnesium oxide is used as a drying agent. See pages 186 - 187

Ionic formulas are based on the ions of the atoms involved. Remember the naming principles above. For example, what is the name of Ca3N2? Ca, the positive ion, is calcium. N, the negative ion, is nitrogen. Drop the end of the anion and add -ide. Calcium nitride

Practice Name the following compounds: NaCl KF BeS SrBr2 Sodium chloride Potassium fluoride Beryllium sulfide Strontium bromide

The Chemical Name and Formula of an Ionic Compound (continued) Writing formulas for ionic compounds: In an ionic compound, the positive charges balance out the negative charges. The ratio of positive:negative charges gives the proper formula. The ratio is always written in reduced form. For example, 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 and 2 P3– ions Mg3P2 See page 188

Try the formula for calcium oxide. calcium is Ca2+ oxygen is O2– 1 Ca2+ ion and 1 O2– ions Ca2O2, which is simplified and written as CaO Calcium oxide, also known as “quicklime” was once produced by cooking limestone in ancient kilns.

Practice Write the formulas for the following compounds: Silver chloride Sodium selenide Lithium sulphide Barium nitride AgCl Na2Se Li2S Ba(NO3)2 (c) McGraw Hill Ryerson 2007

Formula of an Ionic Compound with a Multivalent Metal Some transitional metals are multivalent, meaning they have more than one ion form. On the periodic table, the most common form of the ion is listed on top. In the name of the compound, Roman numerals are used following the positive ion to indicate which ion was used. See pages 189 - 191

For example, what is the formula manganese (III) sulphide? This manganese is Mn3+. sulfur is S2– Lowest common multiple of 3 and 2 is 6 2 Mn3+ ions and 3 S2– ions Mn2S3

Try the name for TiF4 titanium is Ti4+ or Ti3+ fluorine is F– 1 Ti4+ ion and 4 F– ions titanium (IV) fluoride

Practice What is the formula for lead (II) iodide? What is the name of Co2O3? (c) McGraw Hill Ryerson 2007

Polyatomic Ions Some ions, called polyatomic ions, are made up of several atoms joined together with covalent bonds. The whole group has a + or – charge, not the individual atoms. What is the formula of sodium sulphate? Na+ and SO42– Na2SO4 What is the name of the compound KClO? K+ = potassium ClO– = hypochlorite potassium hypochlorite See pages 192 - 193

Practice What is the formula of barium perchlorate? What is the name of (NH4)3PO3?

Names and Formulas of Covalent Compounds Covalent compounds, also called molecules, rely on the chemical formula to reveal the components of the molecule. Covalent compounds are made up of two or more non-metals. Names may reveal the components, but often they do not. Subscripts mean something different in covalent compounds Ionic compounds subscripts show the smallest whole-number ratio between the ions in the compound. Covalent molecules have subscripts that show the actual number of atoms in the molecule. See page 193 (c) McGraw Hill Ryerson 2007

What is the chemical formula for the molecule ethanol? C2H6O, a name that must be memorized or looked up when needed. What is the name of the molecule C12O22H11? Sucrose, also called table sugar.

Naming Binary Covalent Compounds Binary covalent compounds (two non-metal atoms) use a system of prefixes. Prefixes are often used before the atom name to indicate the number of atoms in the molecule. CO = carbon monoxide, CO2 = carbon dioxide Write the most metallic atom (farthest left) first Add -ide to the end of the second atom’s name See pages 194 - 195 (c) McGraw Hill Ryerson 2007

Naming Binary Covalent Compounds What is the chemical formula for the molecule trinitrogen tetrachloride? N3Cl4 What is the name of the molecule Si3P6? Trisilicon hexaphosphide What is the name of the molecule XeF6? Xenon hexafluoride What is the chemical formula for the molecule dinitrogen tetraoxide? N2O4

Comparing Ionic and Covalent Compounds 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. If the compound is covalent: Use the prefix system of naming if the compound is binary and does not start with hydrogen. If there are more than two different elements, or it starts with H, there is probably a different, simpler name for the covalent molecule. If the compound is ionic: Check the metal to see if it is multivalent (add a Roman numeral if it is multivalent). Naming starts with the name of the metal atom. If it ends with a single non-metal, naming will just end in -ide. If it ends in a polyatomic ion, look up the name/formula. See pages 196 - 197

Review To do: Worksheet Take the Section 4.2 Quiz