Atomic Bonding and Molecules Chapter 15 Bonding of atoms makes molecules The Formation of Ions and Ionic Bonds Types of bonds Metallic Bonds Covalent Bonds Polar Covalent Bonds Molecular Polarity and Molecular Attractions Causes of bonding Atoms bond together through their electrons Electrons behave as though they are contained within a series of seven concentric shells Outer shell electrons interact with electrons of other atoms These are the VALENCE electrons Maximum number of electrons in each shell is shown Inner shell fills up before next shell begins to get electrons Full shells are most stable Electron Shells Full electron shells Outer electron shells of noble gases are full In Class Activity 1 Draw the electron shells for the sodium atom around the chemical symbol for sodium What element has the electron structure that sodium would have if it lost one electron? Sodium Ion Formation Ion: An atom that has lost or gained one or more electrons Periodic table Electrons shells in periodic table First three periods 1
Electron Dot Structure A notation showing only the valence electrons surrounding the atomic symbol Electron dot structure pattern In Class Activity 2 ow are electron shell diagrams different from electron dot structure diagrams? Do they both tell you about the valence electrons? Which is easier to draw? In Class Activity 3 Draw the electron dot structure for sodium and chlorine atoms What electron change do you imagine may occur so these elements bond? Water Molecular Ions O + ydronium ion, 3 O + + ydrogen ion Typically formed by the loss or gain of a hydrogen ion, + Ion An atom, molecule, or compound with a different number of protons and electrons More protons: positive CAT ION TE t looks like a plus sign More electrons: negative AN ION Negative has an N in the prefix Both are all one word: anion, cation Ion formation Lose electrons more protons than electrons positive charge Gain electrons More electrons than protons Negative charge More than one can be lost or gained Determine by position in periodic table Electron dot structure pattern Typical ions formed 2
In Class Activity 4 Draw the electron dot structure for a magnesium atom in area to right What is the charge of an ion that is formed from a magnesium atom? Why does it have this sign and amount of charge? Ionic Bonds Electrical force of attraction between oppositely charged ions Ionic Bond Ratios Compounds form in ratios to neutralize charges Question For Thought Is the change of sodium and chlorine atoms to the ionic compound sodium chloride a physical or a chemical change? In Class Activity 5 Write the chemical formula for a compound made of magnesium ions, Mg 2+, and oxygen ions, O 2 Write the chemical formula for a compound made of aluminum ions, Al 3+, and oxygen ions, O 2 Write the chemical formula of the ionic compound calcium fluoride Groups of atoms forming ions Polyatomic ions Bonds within group are covalent Metallic Bonds Nucleus of metal atoms only weakly hold outer electrons Weak attraction allows the electrons to move from one atom to another quite freely Metallic Properties Mobility of electrons results in many properties of metals Conductive electrons move freely Shiny electrons vibrate and reflect light Malleable can move with respect to one another without breaking because electrons in constant motion Alloys electrons shared between unlike types of metal atoms Metallic Alloys An alloy is a mixture of metallic elements. 3
Metal Ores Few metals naturally occur as elements Gold, copper, mercury Most occur as oxides and sulfides Ionic compounds Concentrations of these are ORE Covalent Bonds Atoms are held together by their mutual attraction for shared electrons Covalent Bond Diagrams The covalent bond is represented using a straight line F F F F There are two electrons within a single covalent bond Covalent Water Covalent Ammonia Covalent Methane Multiple covalent bonds are possible if atom has more than one unpaired valence electron Nonpolar Covalent Bonds Electrons are shared evenly when the two atoms are the same element Polar Covalent Bonds Shared unevenly when the bonded atoms are different elements 4
Polar covalent bonds Closer together on the periodic table, less polar bond Further apart on the periodic table, more polar bond Molecules are called dipoles Ionic bonds are extremely polar but not covalent In Class Activity 6 Rank these compounds in order from least polarity (1) to greatest polarity (4) by number below each compound PF, SF, GaF, GeF Molecular Polarity Molecular Attractions Water and salt Water and water Ions Ion-dipole of NaCl attract attraction dipole of water Dipole-dipole attraction Dipoles of water attract one another Electrical attractions between molecules that does not result in bonding Ions Polar molecules Non-polar molecules Some non-polar molecules can be distorted Dipole-Induced into dipoles dipole by polar attractions molecules--oxygen and water Molecules Induced can dipole-induced develop induced dipole dipoles especially attractions if they are large Teflon is nonstick Because the fluorine atoms are non-polar and don t readily become induced dipoles 5