Chem Chapter 7, 8 Williams

Ionic, Metallic, and Covalent Bonding

Types of bonds

Types of bonds

Ionic, Metallic, Covalent (chapter 8), Polar covalent (chapter 8), Coordinate covalent (chapter 8)

If the nucleus has a pull, why don't the electrons crash into it?

It is moving at the speed of light orbiting. If it was static, it would crash into the nucleus. It has momentum.

Valence electrons

These electrons create the ionic bond. These are the electrons that occupy the highest energy (only the “s” and “p” orbitals - can’t be d because d is always in the previous lower energy level)

How many valence electrons do transition metals have

two

how do you determine the number of valence electrons of an element?

look at the last digit of the group number

Lewis Dot Structure

visualization of valence electrons

Pseudo Noble Gas Configuration

an atomic ion that forms that has the same number of electrons as a noble gas.

Why does Hydrogen exist as H2?

the stable configuration of hydrogen is in a duet, which is formed by the sharing of the electrons in TWO hydrogens.

How are ionic compounds created?

they result from the formation of ionic bonds between the atoms

charge of compound

always neutral - ions may have net charge

general form of ionic compound

metal - nonmetal bond

do ionic bonds share electrons?

no - they are transferred

Formula unit

empirical formula of any ionic or covalent network solid compound (ex. NaCl)

salt

any ionic compound

order of elements in formula unit

cation, anion

properties of ionic compounds

Crystalline solid at room temperature because they act as magnets attracted and holding each other together. High melting points (Ex. NaCl: 801ºC), Crystals (ionic compounds) have a very high melting point due to the ions strongly attracting and holding in place. Tends to be soluble in water. Tends to be brittle. Do not conduct heat or electricity in solid, liquid, or aqueous state (pseudo noble gasses: full electron rings, with no valence electrons, and a fixed, rigid position)

Current

moving, charged particle

coordination numbers

the number of atoms that bond to the central atom

what does a lower coordination number imply?

there are fewer things being held together = easier to melt

Bonding in metals

generate properties associated with metals

how does metallic bonding work?

Many of the metals have electrons in the d orbitals. Many of these orbitals are not full of electrons. When metal atoms form bonds, the electrons in the d orbitals move like a wave through the neighboring d orbitals. this is known as the “Sea of electrons” model.

How do metallic bonds hold?

even though they don't have the + and - charge that ionic bonds create, the shared electrons in the D orbitals are being acted upon by many nuclei that it creates the force that holds it together.

Are ionic compounds conductive?

no. there is no space for bonding in the d orbital - one of the elements do not have a d orbital (metal and nonmetal bond) so they stay where they are (no movement of electrons)

properties of metals

Conducts heat, electricity. Ductile and malleable. Bright and shiny. Solids at room temperature (mercury is the exception). High melting point

melting point of ionic compounds vs metallic compounds

the melting point of metals is not nearly as strong as ionic bonds because it doesn't have the transfer of electrons that makes it very stable which is why it is lower but still high bc so many nuclei act upon the electrons that it becomes somewhat stable.

why do metals form crystals?

to utilize space more effectively

what are crystal structures called?

the three in nature are called the unit cell.

3 crystal structures

Simple cubic, Body centered cubic (BCC), Face centered cubic (FCC). Many metals will also incorporate the hexagonal close packing arrangement. This is mostly associated with the BCC and FCC unit cells

Metal alloys

Mixture of two or more atoms. Provides superior performance compared to the pure elements

example of metal alloys

Iron - useful example. When iron is mixed with a small amount of carbon, the materials is much stronger and has more flexibility - steel. When iron is mixed with chromium, carbon, and nickel, it no longer rusts - stainless steel

covalent bonds are between which types of elements?

nonmetal - nonmetal.

molecular compounds

very different compared to ionic compounds. Typically they are liquids or gasses (Oxygen, Water, Carbon dioxide).The molecules are not fixed into a lattice but are independent. Based upon covalent bonds. Atoms in the structure do not have a “localized” charge - neutral

covalent bond description

Electrons in the valence shell are SHARED between the atoms in the bond

non polar covalent

Electrons shared equally

polar covalent

Electrons not shared equally

molecular formula

describes molecules made with covalent bonds (ex. H2O is the molecular formula for water). Molecular Formula shows how many and what type of elements are in the molecular compound. Molecular formulas do not provide information about the structure of the molecule.

net charge of covalent compounds (and ionic)

zero

alcohol functional group

(C)-O-H attached to a carbon means that the molecule is an alcohol in an organic compound (O-H in an inorganic compound)

What does an organic molecule need to have?

a carbon chain (C-C-C-C...)

what do inorganic molecules have

carbon (don't have to be in a chain)

molecular compounds

The chemical formula is the same as the molecular formula. Tends to be liquids or gasses at STP (standard temperature 0º/273 K and pressure 1 ATM/101.3 KPa). They have lower melting and boiling points. Are independent molecules. Share electrons between atoms. Atoms do not have a localized charge

nature of covalent bonds

The overlap of atomic orbitals creates a space where electrons from each atom can be shared to form a covalent bond. The unshared electron pairs occupy electron orbitals that are not overlapping orbitals in the adjacent atoms. these electrons impact the shape of the molecule

hybridization

concept of mixing atomic orbitals to form new hybrid orbitals suitable for the pairing of electrons to form chemical bonds in valence bond theory

what are double and triple bonds based upon?

the geometric shapes of the s and p atomic orbitals, different orbitals overlap creating double and triple bonds

what will carbon always form?

Carbon will always form 4 bonds (CO2 forms two pairs of double bonds)

where can covalent bonds take place?

the outer s and p shells (valence)

where can metallic bonds take place?

d orbitals (shared - sea of electrons)

where do ionic bonds form?

Metals that form bonds in the s and p (transfer of electrons)

Coordinate Covalent Bonds

Established when both electrons are supplied by one of the atoms (Ex. Carbon monoxide - Carbon has an empty p orbital). Sometimes will exceed the octet rule. Ex. SF6 - The sulfur provides the electrons for the additional bonds (coordinate covalent). Generally will only happen with group 3 and below because above that the central atom is too small

where are coordinate covalent bonds commonly found?

polyatomic atoms

Exceptions to the octet rule

In some molecules there are an odd number of electrons or there are not enough to satisfy the octet rule. There will be a single electron in the structure. This means the compound is not stable. In some you don’t have enough electrons. Ex. BF3 is not stable because Boron has 3 valence electrons. Each fluorine has 7. There are 24 in total. Fluorines get stable octets, boron left with only 6.

Polar and nonpolar substances put in solutions

If a substance is polar and you put it in a polar solution, it will dissolve. If you put a non polar substance into a polar solution, it will not dissolve.

Bond Dissasociation Energies

The bond represents the potential energy. The energy is “stored”. Each bond in a double or triple bond increases the energy needed to break the two atoms apart. The bond length, distance between atoms decreases as the number of bonds increases. The larger the bond energy the more stable the molecule.

The energy required to raise 1 g of water 1 degree celsius

1 (energy) calorie NOT food calorie

Valence Shell Electron Pair Repulsion (VSEPR)

Used to predict the 3 dimensional shape of a molecule. Based upon the repulsion of the unshared and shared pair electrons

VSEPR theory bond strengths

Unshared - unshared (strongest). Unshared - shared (medium). Shared - shared (weakest)

Molecular orbitals

When the atomic orbitals associated with a specific atom overlap the atomic orbitals of an adjacent atom, the result is the combination of the two atomic orbitals which is now called a molecular orbital

sigma bond

most bonds - all single bonds. Bond formed along the bond axis (if the overlap of the orbitals falls on the axis drawn between the two nuclei)

pi bond

Bond formed above and below bond axis (or to the side - the overlap of the orbitals hybridize into a molecular orbital that does not fall upon the bond axis)

why can't there be a quadruple pi bond?

When a fourth bond is attempted, the overcrowded electrons between the atoms resist the change so strongly that it requires little, if any, energy. This arrangement is therefore unstable, so a quadruple bond will be essentially impossible. The bonds are facing away from each other, so it is hard to get a quadruple bond.

Bond Polarity

Determined by finding the difference between the electronegativities of the two bonding atoms. Nonpolar: less than 1.0, Polar: 1.0 - 2.0, ionic: 2.0 - 3.2

Hybridization

When molecular orbitals form they hybridize (change shape) so that the molecular orbital is identical even though they come from different overlapping orbitals (for methane, 3 are s and p and one is s and s)

what does the bond polarity create?

a dipole moment. The dipole moment is shown using the lower greek letter delta 𝜹. The dipole moments can be added (vector addition) to determine the net dipole of the molecule Note. nonpolar covalent bonds have a very small or no dipole moment. We use the bond polarity to determine the overall molecular polarity - They are separate!!

Intermolecular Forces (strongest to weakest)

Hydrogen bond

LDF/VDWF

Dipole - Dipole

Dipole - induced dipole

induced dipole - induced dipole

Hydrogen Bonding

H bonding only occurs between hydrogen and an atom with high electronegativity. the electrons from the H will spend more time around the atom with high electronegativity. when the atoms do go back to the 1s orbital of Hydrogen, the bond will break (so it breaks and reforms over and over)

Dipole - Dipole interaction

occurs between two molecules with permanent dipoles. when the positive end and negative end of the two get attracted towards each other it forms the dipole - dipole interaction.

Dipole - induced dipole interaction

occurs when you have a diatomic molecule and another molecule with a fixed dipole. sometimes, the diatomic molecule will be moving slow enough such that it when it comes into contact with the +/- end of the other molecule, the electrons will move to the other side of that molecule, creating a temporary dipole which is where the dipole/induced dipole interaction is created.

induced dipole - induced dipole interaction

occurs when you have two atoms with stable electron configurations that have no net charge on the molecule. for a very short period of time, those electrons may exist on one side of the atom, creating a small dipole moment that causes a chain reaction in all of the other atoms. this creates the induced dipole - induced dipole interaction.

IMF enables the formation of

Surface tension, Liquids, Solids

Network Solids

some compounds with covalent bonds forming solids that have high melting points. Examples

Diamond (vaporize at 3,500º C)

Graphite (vaporize at 3,500º C)

Silicon Carbide (MP at 2,700º C)

Silicon Dioxide (MP at 1,710º C)

Mostly group 14 elements