The correct classifications for sea water, distilled water, brass, and helium respectively are

(a)compound, element, mixture and compound

(b)mixture, element, mixture and compound

(c) mixture, compound, mixture and element

(d) compound, element, compound and mixture

(e) mixture, compound, compound and element

All mixtures (indicate correct statement)

(a) are heterogeneous in appearance

(b) contain different types of molecules

(c) contain two or more pure substances

(d) can be separated only by chemical means

(e) contain more than one physical state

DIMENSIONS AND UNITS

Need to provide a quantitative means of describing the universe.

7 independent dimensions (physical quantities):

1. Mass (m) quantity of matter in a body

2. Length (l) measurement of distance

3. Time (t) measurement of progress of an event

4. Thermodynamic temperature (T). “The condition of a body which determines the transfer of heat to or from that body”

DIMENSIONS AND UNITSDIMENSIONS AND UNITS

5. Amount of substance (n). “The number of specified entities of a pure substance”

6. Electric current (I): “Rate of transfer of electricity”

7. Luminous intensity (Iv): “Rate of transfer of light energy”

Fundamental Property of Dimensions:Two physical quantities having different dimensionscannot be added, subtracted or equated.

All other physical quantities can be expressed in terms of these fundamental dimensions

e.g. volume of a cube = l x l x l = l3

velocity = distance/ time = l/t

Common S.I. prefixes

Prefix Name Meaning

G giga 109

M mega 106

k kilo 103

d deci 10-1

c centi 10-2

m milli 10-3

micro 10-6

n nano 10-9

p pico 10-12

Derived Units

Quantity Definition Derived Unit

Area Length x length m2

Volume Area x length m3

Density Mass/ unit volume kg m-3

Speed Distance/ unit time m s-1

Acceleration Change in speed/ m s-2

unit time

Force Mass x acceleration kg m s-2 (newton, N)

Pressure Force/ unit area kg m-1 s-2 (pascal, Pa)

Energy Force x distance kg m2 s-2 (joule, J )

Difference between mass and amount of substance:

amount of substance is the number of specified entities (e.g. atoms, molecules, etc.)

Entity Number of entities Mass (g)

Hg 6.02 x 1023 atoms 200.59(= 1 mol)

KCl 6.02 x 1023 molecules 74.56(= 1 mol)

SO42- 6.02 x 1023 ions 96.06

(=1 mol)

Accuracy: measure of how close measurement is to its real value

Precision: measure of how close successive measurements are to each other

XXXXX X

X X

X

Precise Precise Imprecise& accurate & inaccurate & inaccurate

Dimensional analysis: a method of reducing physicalquantities to combinations of the 7 basic dimensions

Q1. Dimensions of pressure?

A. Pressure = Force/Area and we already know the dimensions of force are MLt-2. Thus the dimensions of pressure are MLt-2/L2 = ML-1t-2.

Q2. Check the validity of the following equation: PV = nR/T, given units of R to be ML2t-2n-1T-1.

A. Dimensions of L.H.S.: ML-1t-2 . L3 = ML2t-2

Dimensions of R.H.S.: n . ML2t-2n-1T-1 = ML2t-2T-2

Equating both sides does not cancel all terms, thus equation is invalid.

ATOMS AND MOLECULES

Atom:smallest particle of an element which canundergo chemical changes in a reaction

Molecule: smallest particle of a compound which can exist and still retain the chemical properties of the compound.

Structure of the Atom

Size: 0.1 to 0.5 nanometers (1nm = 1x10-9m)

Mass: H atom = 1.67x10-24g = 1.008 atomic mass units (a.m.u.)

C atom = 2x10-23g = 12.000 a.m.u.

Electrical charge: neutral

Composition: contains electrons, protons, and, with the exception of hydrogen, neutrons.

Particle Mass (a.m.u.) Charge e- 0.0005 -1 p+ 1.007 +1 n 1.009 0

Structure of the Atom

Size: 0.1 to 0.5 nanometers (1 nm = 1 x 10-9 m)

Nucleus Electron clouds

~ 5 x 10-15 m

~ 2 x 10-10 m

Nucleus- consists of protons and neutrons

“Life-sized” model of the atom

“Scaled up” electron mass

Electron = 0.0005 a.m.u. Proton = 1.0070 a.m.u.“Model proton” = 65 kg “Model electron” = 32 g

“Scaled up” atomic radius

Nuclear diameter = 5 x 10-15m Atomic diameter = 2 x 10-10 m “Model nucleus” radius = 1 m “Model atomic” radius = 40 km

Q. A speck of carbon contains ca. 1019 atoms and the diameter of a carbon atom is 1.5 x 10-10 m. If the circumference of the earth is 40,075 km, how many times around the earth would a line of single carbon atoms extend?

A. Length = 1019 x 1.5 x 10-10 m = 1.5 x 109 m.

# times = 1.5 x 109/40075 x 103 = 37.4

Iron atoms on acopper crystal

Xenon atoms on nickel

Carbon monoxide molecules on platinum crystal

Atomic number:number of protons in an atom. Symbol: Z

Atomic mass: mass of an atom in a.m.u. (number of protons + neutrons in an atom). Symbol: A

Atom e- p+ n Z A (a.m.u.)

H 1 1 0 1 1.008

Li 3 3 4 3 7.016

C 6 6 6 6 12.000

U 92 92 146 92 238.05

Conventional Notation for Chemical Symbols

Cl35

17

-

2

Mass number Number and sign of charge

Atomic number Number of atoms in entity

Examples: He42 OH- CO

32-

Ions: atoms or molecules which have gained or lost oneor more electrons

Isotopes: atoms of the same element which have different masses, i.e. different numbers of neutrons

Examples of ions: H+ H- NO3-

Examples of isotopes: H11

H12

H31

Hydrogen

Deuterium

Tritium