solids, liquids, gases, review

8/6/2019 Solids, Liquids, Gases, Review

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Solids, Liquids, and Gasses

Review Low densities High compressibility Completely fill container

Solids High densities Slight compressibility Rigid, maintain shape

Liquids Properties found between solids and gasses Closer to solids than gasses Energy required to melt 1 molH2O=6kJ/mol Energy required to vaporize 1mol H2O = 41 kJ/mol It takes a lot more energy to change from a liquid to a gas than a solid to a

liquid

We can also look at densities of each phase of H2O to see how solids andliquids are closely related

Density of H2O Solid (ice) = .9168 g/cm3 Liquid(water) = .9971 g/cm3 Gas (water vapor) = 5.88 x 10- 4 g/cm3 Water in its gaseous state is 2000 times more dense than water in

its liquid state

Water in solid state and liquid state have similar densitiesWater and Phase Changes

97% of earths water is found in the oceans Colorless, odorless Freezes at 0oC and vaporizes at 100oC For substances to change state, heat(Q) must be added or

removed

Water is unique in that its solid state is less dense than liquidstate (Why?)


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H2O and Density Density is equal to mass of a substance divided by its volume

(D=m/v)

As a sample of water freezes, its volume increases while its massis relatively unchanged.

This increase in volume brings on a decrease in density This is why ice cubes float in water

Energy Changes for Changes in State During a phase change, NO chemical(intramolecular) bonds are broken. A phase change involves physical changes only Bonds that hold a single molecule together are called intramolecular

bonds

The bonds that occur between molecules and cause them to aggregate toform liquids and solids are called intermolecular bonds

Phase Change and Energy Energy required to melt one mole of a substance is called molar heat of

fusion

For ice, the molar heat of fusion is 6.02kJ/mol Energy required to change 1 mole of a liquid to its vapor(gas) is called the

molar heat of vaporization

For water, the molar heat of vaporization is 40.6kJ/mol It takes more energy (almost 7 times as much) to change 1mole of water

into a gas than it does to melt one mole of ice

Why Such a Difference? To separate molecules into a gas, virtually all intermolecular

bonds must be overcome.

The stronger the intermolecular bondsPolar molecule

two or more nonmetals that have unequal sharing of electronscausing a positive and negative charge on opposite ends of the

molecule.

Caused by large differences in electronegativity of two or moreelements


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Electronegativity

Nonpolar molecules two or more nonmetals that have equal sharing of electrons

throughout the moleculeNonpolar molecules usually have elements that are close in

electronegativity

Polar/Nonpolar Difference A nonpolar molecule is distinguish from a polar molecule by there

difference in electronegativity

If the electronegativity difference (usually called EN) is less than 0.5,then the bond is nonpolar

If the EN is between 0.5 and 1.6, the bond is considered polar If the EN is greater than 2.0, the the bond is ionic. If the EN is between 1.6 and 2.0 and if a metal is involved, then the bond

is considered ionic. If only nonmetals are involved, the bond is considered

polar.

Types of Intermolecular Bonds

1. Dispersion Bonds Also called London Forces, these are weak bonds that result from

temporary shifts(dipole moment) in the density of the electrons in the

electron cloud. Exist in all molecules Its the only intermolecular bond in non-polar covalent molecules Larger the molecule, the stronger the dispersion bond

Dispersion Bonds

Multiple Dispersion Bonds

Examples of Dispersion Bonds

Boiling Points of Noble GasesGraphite Structure

Dispersion Bonding and Molecules

Types of Intermolecular Bonds


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2. Dipole-Dipole Bonds exist between polar molecules only Stronger than dispersion bonds Polar molecules have a permanent positive end and a permanent negative

end Polar molecules are composed of a highly electronegative element along

with elements of low electronegativity.

There is a special type of dipole-dipole bond called a hydrogen bondHydrogen Bonding

Strongest type of intermolecular bond Type of dipole-dipole bond Exist between hydrogen on one molecule bonding with one three elements

on another molecule

Those three elements are nitrogen, oxygen, and fluorine Lets look at some examples of hydrogen bonding

Water and Hydrogen Bonds

Water and Hydrogen Bonds

Hydrogen Bond Example

Hydrogen Bonding and DNA Hydrogen bonds hold the base pairs of DNA together

DNA

Intermolecular Bond Review

Types of Solids Crystalline- have a regular repeating pattern (lattice structure) Amorphous random, unorganized patternCrystalline Solids All have high melting points Three types: ionic solids, molecular solids, and atomic solids

Ionic Solids


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Composed of ions (usually a metal paired with a nonmetal orpolyatomic anion)

Molecular SolidsNo ions are present (usually composed of all nonmetals

covalently bonded)

Atomic Solids Solids composed of only one element covalently bonded to each

other

Bonding in Solids Ionic solids- high melting points, held together by strong oppositelycharged ions/examples include NaCl, BaSO4, NH4F

Molecular solids- low melting points, held together by weakintermolecular bonding(dispersion, dipole-dipole)/ examples include ice,

dry ice(solid CO2), sugar

Atomic solids- lots of variation, properties depend on radius, valence,electron structure, etc./ examples include diamond, copper, iodine

Amorphous SolidsNo regular repeating pattern Dont hold shape well if temperature is increased Examples include tar, wax, plastic, glass, rubber

http://www.docstoc.com/docs/34764229/Solids-and-Liquids

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