Bond, Chemical Bond CPS Chemistry Part 1

What is bond? A chemical bond is an attractive force between atoms that connects them together. This attractive force comes from the absence or abundance of electrons in the outer most electron level of an atom, it involves the valance electrons valance electrons Atoms bond so their valence electrons will redistribute in ways that make the atom more stable

Types of connections Types of Bonds between atoms to form molecules and compounds Ionic Covalent Polar Non Polar Metallic Intermolecular Forces Forces of attraction between molecules Dipole-Dipole Hydrogen Bonding London Dispersion Forces

Ionic Bonds Ionic Bonding Atoms either loose or gain electrons to form complete outer energy levels It is the result of large numbers of cations and anions that are attracted due to electrical imbalancescationsanions

Covalent bonding Covalent Bonding – when electrons are shared between atoms, think cooperation… Two types Polar & Non Polar

Non-Polar Covalent Bond Electrons are shared evenly between both atoms the charge is evenly distributed around the molecule

Polar-Covalent Bond While the electrons are shared, they are unevenly distributed around the molecule One side of the molecule is more positive than the other side (has less electrons)

Metallic Bond The movement of the free electrons means that metallic bonded materials have good thermal and electrical conduction. In metallic bonding instead of sharing electrons between two atoms the electrons in the outer shells are shared amongst all the atoms in a lattice with all the atoms positively charge. These atoms are attracted to the negatively charged 'cloud' of electrons.

Bond Properties - Covalent Forms molecules Low melting points & boiling points Softer, more flexible Doesn’t conduct electricity Doesn’t easily dissolve in water Exceptions HCl, NH 3, sugars Have weak molecular forces between molecules Examples: H 2 O, O 2, CH 4

Bond Properties - Ionic Creates compounds High melting points & boiling points Creates rigid crystalline solids Conducts electricity Soluble in water Has strong forces between ionic compounds Will conduct electricity when molten or dissolved in water Examples: NaCl, CaF, KCl

Metallic Bond Properties Metals are good conductors of heat and electricity. This is directly due to the mobility of the electrons. The "cement" effect of the electrons determines the hardness of the metal. Some metals are harder than others; the strength of the "cement" varies from metal to metal. Metals are lustrous. This is due to the uniform way that the valence electrons of the metal absorb and re-emit light energy. Metals are malleable (can be flattened) and ductile (can be drawn into wires) because of the way the metal cations and electrons can "flow" around each other, without breaking the crystal structure.

What type? Using the electronegativity of elements, you can determine the type of bond createdelectronegativity By finding the difference (subtract one from the other) will express what type of bond is made Difference = 0  0.3 Nonpolar Covalent Difference = 0.3  1.7: Polar Covalent Difference = 1.8  and above Ionic

Electronegativity chart

A Way to remember… Think of electrons as bones….What would your dog do? Ionic bonds: One big greedy thief dog! Non-Polar Covalent bonds: Dogs of equal strength. Polar Covalent bonds: Unevenly matched but willing to share. Metallic bonds: Mellow dogs with plenty of bones to go around.

Intermolecular Forces Once a molecule is made, it does not live in isolation, it will connect with other molecules Intermolecular forces is the forces of attraction between molecules Types Dipole-Dipole Hydrogen bonding London Dispersion Forces

Dipole-Dipole A dipole ( δ ) is created by equal in magnitude, but opposite in charge molecules, separated by a short distance The direction of a dipole is from its positive side to its negative side They are short range forces, only affect near by molecules Strongest of the intermolecular forces Br F

Hydrogen Bonding A type of dipole-dipole bonding A hydrogen atom bonded to a highly electronegative atom, and then attracted to unshared pair of electrons of a near by electronegative molecule Examples HF, Water δ+δ+ δ+δ+ δ-δ- Water

London Dispersion Intermolecular attraction resulting from the constant motion of electrons and creations of instantaneous dipoles. This is the only type of attraction detected with Noble Gasses & non-polar molecules It is a relatively weak force

Louis Structure & Electron Dot A short hand representation of the valence electrons available for bonding The “goal” is to have a complete set of valence electrons Each group has its valence number 1-8

Electron Dot Valence ElectronE-dotExample 1X Na 2X Mg 3X B 4X C 5X N 6X O 7X F 8XNe

Louis Structure You can use electron dot diagram to show molecules A shared pair : can be show by – H:H or H-H A double shared pair :: can be shown by = C::O or C = O A triple shared pair ::: can be shown by = N:::N or N=N

Terms and Extras If you need further definitions and explanations look at the slides beyond this point

molecule A molecule is a neutral group of atoms held together by covalent bonds

Electronegativity Electronegativity is a measure of the tendency of an atom to attract a bonding pair of electrons.

Valence Electron Electrons that are in the outermost energy level of the atom Valance electrons are either shared or gained/lost in chemical bonds

Ions Ion – an atom with a charge, either positive or negative due to the number of electrons (negative charge) it has in relation to the number of protons (positive charge) Cation – an ion with a positive charge, so it has less electrons than a neutral atom of that element, usually non-metals Anion – an ion with a negative charge, so it has more electrons than a neutral atom of that element, usually metals