Northern Kentucky University Lecture Presentation Chapter 6 How Atoms Bond Bradley Sieve Northern Kentucky University Highland Heights, KY

6.1 Electron-Dot Structures Valence Electrons Outermost electrons of an atom Valence Shell The outer shell containing electrons Electron-Dot Structure Convenient notation showing the valence electrons

6.1 Electron-Dot Structures Model showing the valence electron arrangements within an atom Explains ionic and covalent bonding

6.1 Electron-Dot Structures Important information in the dot-diagram Number of valence electrons Number of paired and unpaired electrons

6.1 Electron-Dot Structures Nonbonding Electron Pairs Nonbonding electron pairs do not normally form bonds Unpaired Electrons Have a strong tendency to form bonds Become paired as they form bonds

6.1 Electron-Dot Structures Electron Spin Causes of electron pairing Two types of spin Clockwise Counterclockwise

Concept Check Where are valence electrons located? Why are they important?

Concept Check Valence electrons are located in the outermost occupied shell of an atom. They are important because they play a leading role in determining the chemical properties of the atom.

6.2 Atoms Can Lose or Gain Electrons to Become Ions Electrons can gain or lose electrons Unequal number of electrons and protons results in a charge Atom with a charge is called an ion A positive charge is seen when an atom has more protons, called a cation A negative charge is seen when an atom has more electrons, referred to as an anion Superscripts are used to denote charges

6.2 Atoms Can Lose or Gain Electrons to Become Ions

6.2 Atoms Can Lose or Gain Electrons to Become Ions

6.2 Atoms Can Lose or Gain Electrons to Become Ions Atoms tend to lose or gain electrons to reach a noble gas shell model Atom’s model matches a noble gas’s model Atoms with few electrons tend to lose electrons Atoms with many electrons tend to gain electrons

6.2 Atoms Can Lose or Gain Electrons to Become Ions

Concept Check What type of ion does the magnesium atom, Mg, tend to form?

Concept Check The magnesium atom (atomic number 12) is found in group 2 and has two valence electrons to lose. Therefore, it tends to form the 2+ ion.

6.2 Atoms Can Lose or Gain Electrons to Become Ions Additional notes for noble gas shell model Noble gas atoms do not tend to form ions Already have filler outermost shells Noble gas shell model works well for groups 1, 2, and 13–18 Groups 3–12 are more complicated

6.2 Atoms Can Lose or Gain Electrons to Become Ions Molecules can form ions Normally occurs with the addition of an H+ Remember H+ is simply a proton Referred to as polyatomic ions

6.2 Atoms Can Lose or Gain Electrons to Become Ions Common Polyatomic Ions

6.3 Ionic Bonds Result from a Transfer of Electrons When an atom that tends to lose electrons pairs with one that tends to gain electrons, an ionic bond is formed Ionic bond is the electric force of attraction between two oppositely charged ions

6.3 Ionic Bonds Result from a Transfer of Electrons

6.3 Ionic Bonds Result from a Transfer of Electrons Ionic Compound A compound containing ions Typically form with elements from different sides of the periodic table Metals tend to exhibit positive charges Nonmetals tend to exhibit negative charges Positive and negative charges must balance Processes properties different from those of the original elements

6.3 Ionic Bonds Result from a Transfer of Electrons

6.3 Ionic Bonds Result from a Transfer of Electrons

Concept Check What is the chemical formula for the ionic compound magnesium oxide?

Concept Check Because magnesium is a group 2 element, you know a magnesium atom must lose two electrons to form a Mg2+ ion. Because oxygen is a group 16 element, an oxygen atom gains two electrons to form an O2− ion. These charges balance in a one-to-one ratio, so the formula for magnesium oxide is MgO.

6.3 Ionic Bonds Result from a Transfer of Electrons Ionic Crystal Three-dimensional arrangement of ions in an ionic compound Give rise to macroscopic crystal shapes

6.4 The Electrons of Metallic Bonds Are Loosely Held Electrons are loosely held and easily dislodged Electrons flow freely through metal ions

6.4 The Electrons of Metallic Bonds Are Loosely Held Alloy Two or more metals held together with metallic bonding White gold is one example of an alloy

6.4 The Electrons of Metallic Bonds Are Loosely Held Metals in Nature Native metal—metal found pure in nature Most are found as compounds Ores Geologic deposits containing high concentrations of metal-containing compounds

6.4 The Electrons of Metallic Bonds Are Loosely Held

6.5 Covalent Bonds Result from a Sharing of Electrons Bond formed through sharing of valence electrons

6.5 Covalent Bonds Result from a Sharing of Electrons Covalent Compound Substance held together by covalent bonds A molecule is the fundamental unit of covalent compounds

6.5 Covalent Bonds Result from a Sharing of Electrons Electron-dot structures for covalent compounds Nonbonding pairs are pairs on single atom Bonding pairs are shared between two atoms

6.5 Covalent Bonds Result from a Sharing of Electrons Primarily in nonmetal pairings H tends to form covalent compounds Line represents a bonding pair

6.5 Covalent Bonds Result from a Sharing of Electrons

6.5 Covalent Bonds Result from a Sharing of Electrons Diamond Unusual C covalent compound Each carbon is bound to four other carbons Very strong and rigid structure

Concept Check How many electrons make up a covalent bond?

Concept Check Two—one from each participating atom

6.5 Covalent Bonds Result from a Sharing of Electrons Multiple Bonds When more than two electrons are shared Double bond is sharing of four electrons Triple bond is sharing of six electrons

6.5 Covalent Bonds Result from a Sharing of Electrons Covalent Bonding in Polyatomic Ions Comprised of covalent bonding and an overall charge

6.6 Valence Electrons Determine Molecular Shape Valence-shell electron-pair repulsion Also called VSEPR Electron pairs arrange so they are as far apart as possible Result of simple electrostatic repulsions Must consider three-dimensional space

6.6 Valence Electrons Determine Molecular Shape Methane shape (CH4)

6.6 Valence Electrons Determine Molecular Shape Methane shape (CH4)

6.6 Valence Electrons Determine Molecular Shape

6.6 Valence Electrons Determine Molecular Shape Molecular shape is defined by the substituent atoms Substituent atom is an atom or a lone pair on the central atom Two steps to finding shape Position all substituents around central atom Ignore nonbonding pairs and determine shape

6.6 Valence Electrons Determine Molecular Shape

Concept Check What is the shape of a chlorine trifluoride molecule, ClF3?

Concept Check In the shape of chlorine trifluoride, all four atoms are in the same plane. They form a triangle having a fluorine atom at each corner and the chlorine atom sitting at the midpoint on one side.

6.7 Polar Covalent Compounds―Uneven Sharing of Electrons Sharing of electrons is not always equal Uneven sharing leads to polar covalent bonds Separation of charges is called a dipole

6.7 Polar Covalent Compounds―Uneven Sharing of Electrons Electronegativity Ability of an atom to tug on bonding electrons The greater the electronegativity, the greater its ability to pull electrons toward itself Highest values in upper right of the periodic table

6.7 Polar Covalent Compounds―Uneven Sharing of Electrons

6.7 Polar Covalent Compounds―Uneven Sharing of Electrons Types of Covalent Bonds Nonpolar bond The two atoms exhibit the same electronegativity Does not exhibit a dipole Polar bond The two atoms differ in electronegativity Does exhibit a dipole

6.7 Polar Covalent Compounds―Uneven Sharing of Electrons

6.8 Molecular Polarity―Uneven Distribution of Electrons Polarity in molecules depends on the three-dimensional shape of the molecule Must consider both strength of dipole and direction of dipole If the dipoles cancel completely, molecule is nonpolar; if not, then molecule is polar

6.8 Molecular Polarity―Uneven Distribution of Electrons CO2 is nonpolar

6.8 Molecular Polarity―Uneven Distribution of Electrons BF3 is nonpolar

6.8 Molecular Polarity―Uneven Distribution of Electrons When forces are unbalanced, the molecule is polar

6.8 Molecular Polarity―Uneven Distribution of Electrons Water is polar

6.8 Molecular Polarity―Uneven Distribution of Electrons Polar molecules can be thought of as “sticky” The different charges are attracted to each other The stronger the interactions, the higher the boiling and melting points

6.8 Molecular Polarity―Uneven Distribution of Electrons Water molecules attract one another because each contains slightly positive and slightly negative sides

6.8 Molecular Polarity―Uneven Distribution of Electrons