Atoms, Molecules, And Water

8/2/2019 Atoms, Molecules, And Water

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Atoms, Molecules, and Water

I. ElementsA. Cant be broken down by ordinary chemical reactionsB. Chemical symbol

a.

Ex) Na, O, CC. C, H, O, Na. 96% of the mass of most living organisms.

II. Atomic StructureA. AtomB. Subatomic particles

a. Protoni. Positive unit of charge, in atomic nucleus

b. Neutroni. No charge, in atomic nucleus

c. Electroni.

Negative unit of charge, outside of nucleus

Atoms = neutral in charge (unless otherwise noted)# of protons = # of electrons

C. Atomic Numbera. Determined by # of protons in nucleusb. All atoms of a particular element have the same atomic number defines

element

D. Atomic Massa. Protons and neutrons

i. Both have same mass 1.7 x 10-24g = 1 Dalton = 1 amub. Electron mass is 1/1800 mass of protonc. Atomic mass = # of protons + # of neutronsd. Hsimplest atom. 1 proton, 0 neutrons

E. Isotopea. Form of an atom with different # of neutrons but same # of protons and electrons same atomic number

different atomic mass

H isotope can substitute for ordinary H.

H-2 = deuterium H-3 = tritium

- radioactive unstable, nucleus breaks down,decay, emits radiation

III. MoleculesA. Compound in which 2 or more atoms combined in a fixed ratio and joined stronglystable particle

B. Chemical formula


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a. Type of atomsb. How many of each atomc. Molecular mass

i. Sum of atomic masses of component atomsd. Chemical equations

i.

Described chemical reactionii. Ex) reactants productsIV. Chemical BondsA. Electrons

a. Move around nucleus in orbitalsb. Valence electrons

i. Outermost electronsii. Occupy valence shell

iii. H and He valence shell is full with 2 electronsiv. All other atoms valence shell is full of 8 electrons

B. Bondsa.

Result of how atoms share electronsC. Bond energy

a. Amount of chemical energyi. Energy necessary to break a chemical bond

1. By forming bondscells store energy2. By breaking bonds cells release energy

D. Covalent bonda. Sharing of electrons between atoms

i. Strong bondii. Results in each atom having a filled valence shell

b. Each type of atom can form a characteristic # of bonds with other atomsc. Electronegativity

i. Measure of an atoms attraction for electrons in chemical bonds.ii. The more electronegative an atom, the more strongly it pulls electrons

towards itself.

iii. Some atoms in covalent bonds are electronically greedy.d. Nonpolar Covalent Bond

i. Occurs between atoms with some electronegativityii. Electrons shared equally

e. Polar covalent bondi. Occurs between atoms that differ in electronegativity

ii. One end of bond is partial positive charge, other end is partial negativef. Absolute amount of electrons is not important. Difference between 2 atoms is

important.i. If same electrons, shared equally nonpolar covalent bond

ii. If different < 2 electrons shared unequally polar covalent bondiii. If difference >2 electron is captured ionic bond

E. Ionic Bonda. Ionelectronically charged atom or group of atomsb. Anion1 or more units of electrons, negative charge, extra electron


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c. Cationpositive charge, loses electrond. Like charge repel. Opposite charge attracte. Ionic bond between anion and cation.

i. Ex) Na+ + Cl- = NaClf. Hydrophilic- dissolves in water

F.

Hydrogen Bond Fig 2-13a. When H combines with electronegative atom, the H acquires a partial + chargeb. H tends to bond with atom that has negative chargec. H2O tends to bond with atom that has partial negative charge.d. H2O molecules attract with each other via H bondse. Each H2O molecule can form H bonds with 4 other H2O molecules.f. H bonds not as strong as covalent bondg. Collectively strong when there are many

V. H2O- H bonding responsible for many physical properties of water

A. Cohesionstick to itself Fig 2-15a.

Surface tensioni. Measure of how difficult it is to stretch or break surface of a liquid

b. Interfere between water and air, H2O molecules very orderedc. Hbonds to each other + to H2O below

B. Adhesiona. Sticks to other substances

i. Ex) capillary action Fig 2-141. Due to cohesive + adhesive properties2. Capillary actiontendency of H2O to rise in small spaces of

hydrophilic materialsC. Maintain stable temperatures

a. H2O has high specific heat

i. Specific heatamount of heat that has to be absorbed in order to raise 1gof a substance 1C

ii. Raise temperature adding heat energy1. molecules move faster2. Bonds break.

iii. High specific heart of water need 1g amount of heat energy must besupplied to raise temperature.

iv. Lots of energy needed to break H-bonds between H2O molecules.b. H2O has high heat of vaporization.

i. Quantity of heat that a liquid must absorb for 1g to be converted fromliquid to gas

ii. Because of H bonding, H2O molecules must have lots of energy to escapefrom surface of liquid.

iii. Molecules that escape takes heat with them1. surface of liquid is cooler

a. evaporative coolingc. Ice floats

i. Ice crystals are less dense thab liquid H2O H bonding


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ii. 1 H2O molecule forms up to 4 h-bonds Fig 2-131. Liquid form 37C

a. ~ 15% of H2O molecules are bonded to 4 partners2. Ice - 0C

a. All H2O molecules bonded to 4 particlei.

Molecules move apart, prevents bodies of waterfrom freezing solid from bottom Fig 2-16

VI. Acids + Bases (Section 2.6)A. Acid

a. Dissociates in solution to yield H+ and an anioni. hydrogen ion donor = proton donor

ii. Increase H+ concentration in solutioniii. Acidic solution high concentration of H+

B. Basea. H+ acceptorb. Decreases in H+ concentration of solutionc.

Basic solution has low concentration of H

+

C. PHa. Negative log(base 10) of H+ concentration

i. pH = -log10[H+]

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Atoms, Molecules, And Water