GENERAL CHEMISTRY

Isotopes, Electrons and Orbitals.

Electron Configuration and Peridic

Table

Hydrogen 1.000000

Helium 0.097

Oxygen 0.00085

Carbon 0.00035

Neon 0.00012

Nitrogen 0.00011

....

Relative distribution of elements in the
Universe

MATTER and ENERGY

MATTER is anything that has mass

and occupies space.

ENERGY is defined as the capacity

to do work or to transfer heat.

♦
A body in motion possesses energy

because of its motion (

KINETIC

ENERGY

) and because of its position

or composition (

POTENTIAL ENERGY

).

The Law of Conservation of

Matter

There is no observable change in

the quantity of matter during a
chemical reaction or during a
physical change.

The Law of Conservation of

Energy

Energy cannot be created or

destroyed in a chemical reaction
or in a physical change. It can be
only converted from one form to
another.

The Law of Conservation of

Matter

and Energy

The combined amount of matter and

energy in the Universe is
constant.

E = mc

2

MIXTURES

MATTER:

Heterogenou
s

Homogenous
(solutions)

Both separable by chemical and physical
means

and

PURE
SUBSTANCES:

Compounds (molecules) → Elements
(atoms)

/
\

A COMPOUND is a substance that can be decomposed by

chemical means into simpler substances, always in the
same ratio by mass.

An ELEMENT is a substance that cannot be decomposed

into simpler substances by chemical changes.

The PHYSICAL CHANGE

occurs with no change in

chemical composition

.

In any CHEMICAL CHANGE:

(1) one or more substances are used up (at least

partially),
(2) one or more substances are formed,

(3) energy is absorbed or released.

Physical properties can be observed in the absense of

any change in composition.

Chemical properties are properties exhibited by matter as

it undergoes changes in composition.

DALTON’S ATOMIC THEORY

• An element is composed of extremely small

indivisible particles called

atoms

.

• All atoms of a given element have identical

properties, which differ from those of other

elements.

• Compounds are formed when atoms of

different elements combine with each other

in simple numerical ratios (

molecules

).

• The relative numbers and kinds of atoms

are constant in a given compound.

How were nuclei found ?

 Rutherford concluded that

the majority of the mass was

concentrated in a minute, positively charged region

(the nucleus/

central charge) surrounded by electrons. When a (positive) alpha particle
approached sufficiently close to the nucleus, it was repelled strongly
enough to rebound at high angles.

NUCLEAR STABILITY

Particle

Mass Charge

Electron (e

-

) 0.00055 amu 1-

Proton (p or p

+

)

1.0073 amu 1+

Neutron (n or n

0

)

1.0087 amu 0

Mass defect = (sum of masses of all e

-

, p

+

and n

0

) – (actual mass of

atom)

e.g.

35

Cl consists of 17 electrons, 17 protons and 18 neutrons

Mass defect = 17·(0.00055) + 17·(1.0073) + 18·(1.0087) – 34.9689

(actual mass of

35

Cl)

= 0.321 amu

E = mc

2

, → the NUCLEAR BINDING ENERGY

E(0.321g) → 2.8910

13

Jmol

-1

= energy that can heat 76 000 tons of

water from 0 to100

o

C.

ATOMIC NUMBER and MASS

NUMBER

The ATOMIC NUMBER of an atom is

equal to the number of protons in its
nucleus.

The MASS NUMBER of an atom is the

sum of the number of protons and
the number of neutrons in its
nucleus.

Nuclide Symbol

A

MN

AN

ATOMIC WEIGHT SCALE

The ATOMIC WEIGHT SCALE is based on the

carbon-12

isotope

, whose mass is assigned a value exactly 12 amu

(atomic mass units).

The ATOMIC WEIGHT of an element is defined as the weighted

average of the masses of its constituent isotopes, e.g.

Isotope

% Abubdance

Mass(amu)

24

Mg

78.70

23.98504

25

Mg

10.13

24.98584

26

Mg

11.17

25.98259

At. Wt. = 0.7870(23.98504) + 0.1013(24.98584) +

0.1117(25.98259) = 24.31 amu

Atomic Spectroscopy

∆E = h

h – Planck’s constant
 – frequency ( c = λ·  )

Atomic spectra in the visible region for some elements:
a) emission spectra for H, Hg, Ne,
b) adsorption spectrum for H.
Compare the positions of the lines in H spectra.

The Schrödinger

Equation

 - wave function, r

2



2

– electron probability density or electron

density,

r

2



2

volume element = probability of finding electron in that

element

E – energy of the system, V – potential, x,y,z - coordinates

This is differential equation; solutions:  wave functions

QUANTUM NUMBERS

• The principal quantum number, n (the energy level

an electron occupies),

n = 1,2,3,...energy levels

.

• The subsidiary (or azimuthal) quantum number l

(determines the geometric shape of an orbital) ,

l = 0, 1, 2, ...(n-1); s, p, d, f – sublevels

.

• The magnetic quantum number, m

l

(is related to

the spatial orientation of an atomic orbital),

m

l

= -l,...,0,...+l; p

x

, p

y

, p

z

for m

l

= -1,0,+1.

• The spin quantum number, m

s

(determins the spin

of an electron)

m

s

=±½; α, β – states

.

Atomic s-orbitals

Atomic p-orbitals

Atomic d-orbitals

Atomic f-

orbitals

Comparison of energy
of electrons occupying
the atomic orbitals in
an atom.

The lower energy is
the stronger is the
attraction.

The order of filling
atomic orbitals by
electrons

Electronic configuration

FIRST IONIZATION

POTENTIAL

The first ionization energy (IE

1

) is the minimum

amount of energy required to remove the most loosely
bound electron from an isolated gaseous atom to form an
ion with 1+ charge.

e.g.
Ca

(g)

+ 590 kJ → Ca

+(g)

+ e

-

590 kJ/mol

is the

first ionization potential
for Ca.

ELECTRON AFFINITY

The electron affinity (EA) of an

element is defined as the amount of

energy absorbed when an electron is

added to an isolated gaseous atom to

form an ion with a 1- charge.

Be

(g)

+ e

-

+ 241 kJ → Be

-(g)

(energy is absorbed)

EA = 241 kJ/mol (endothermic)

Cl

(g)

+ e

-

→ Cl

-(g)

+ 348 kJ

(energy is released)

EA = -348 kJ/mol (exothermic)

ELECTRONEGATIVITY

The electronegativity of an element is

a measure of the relative tendency
of an atom to attract electrons to
itself when it is chemically combined
with another atom.

max. 4.0 for F and min. 0.8 for Cs (also

Fr)