Summary of the Atom atoms are the smallest particles that can be uniquely associated with an element Atoms cannot break down further by chemical means.

Summary of the Atom• atoms are the smallest particles that can be uniquely

associated with an element• Atoms cannot break down further by chemical means.• each element has unique atoms • atoms are composed of e-, p and n• atoms are electrically neutral (# of e- = # of p)• for a single element, isotopes differ only in number of

n (neutrons)• atoms have characteristic masses (atomic weights)• atoms combine with one another in definite, whole

number proportions to make compounds

~ 10-10 m

nucleusMass 9 x 10Mass 9 x 10-31-31 kg kg Mass > 10Mass > 10-26-26 kg kg

electron

~ 1 – 7 x 10-15 m (1 – 7 fermi)

atoms are dominantly empty space:

If an oxygen atom had a total radius of 100 km, the nucleus

would be a ~1 m diameter sphere in

the middle.

electron orbits

The Spacious Atom

In a simplistic model, electrons float around the nucleus in energy levels called shells.

As the number of

electrons increases,

they start to fill shells

farther out from the

nucleus.

In most cases,

electrons are lost or

gained only from the

outermost shell.

electron orbits

Electrons in Orbit

AtomAtom

NucleusNucleus

Most of the atom is…

• empty space!

The Nuclear Modelof the atom

• Mass of an electron is approximately 1/1840th of a

proton or neutron.

• Mass of a neutron is very close to the mass of a proton.

• 1 atomic mass unit (amu or u)=

1.66054x10-24g

• 1 g= 6.022 x1023amu• amu is defined by assigning a mass of exactly 12

amu to an atom of C-12 isotope.

1 amu (atomic mass unit) is…

• 1/12th of the mass of one carbon-12 atom.

Most of the mass of the atom is…

• formed by the nucleus.

Subatomic Particles

Particle Symbol Charge RelativeMass(unit)

Electron e- 1- 0

Proton p+ 1+ 1

Neutron n 0 1

Atomic Number, Z (nuclear charge)

11NaAtomic Number

Symbol

is the total number of protons in the atom.

Atoms are identified by their proton numbers.

All atoms of an element have the same number of protons

11

Na

11 protons

Sodium

Number of Electrons

If an atom is neutral ;The net charge on the atom is zeroNumber of protons = Number of electronsAtomic number = Number of electrons in a

neutral atom

Ions• have a net electrical charge since the total

number of electrons isn’t equal to the number of protons.

• can be anions (e->p+ ;formed as a result of gaining electrons; negatively charged), cations (p+>e-;formed as a result of losing electrons; positively charged).

• e- + q(charge of the ion) = proton number

• In chemical rxns, atoms never gain or lose protons. It’s the interaction of electrons.

Mass Number, A (nucleon number)

Counts the number

of

protons and neutrons

in an atom

A= p+ + n0

Protons and neutrons (together) are called “nucleons.”

Atomic Symbols

Show the mass number and atomic number

Give the symbol of the element

23Na

11

(Z)atomic number

(A)mass number

sodium-23

Notation for Atoms

12C13C C

only one isotope of carbon

all isotopes of carbon

only one isotope of carbon

Basic Definitions• “atomic number” = number of protons in the

nucleus;

• “mass number” = sum of protons + neutrons in the nucleus

• “isotopic mass” = mass of a single isotope

More Atomic Symbols

16 31 65

O P Zn

8 15 30

8 p+ 15 p+ 30 p+

8 n 16 n 35 n8 e- 15 e- 30 e-

Learning check

For the ion find

a)Nuclear charge

b)Mass number

c)Electron number

d)Neutron number

23920X

Learning checka) Find the value of unknown quantities in the

table given below.

b) Classify each particle, X, Y, and Z as Cation, Anion and Neutral atom.

Homework!

• Prepare the flash cards having the symbol of the atom on one side and the name on the other side for the first 20 elements on Page 33 in your textbook.

Isotopes

Atoms with the same number of protons,

but different numbers of neutrons.

Atoms of the same element (same atomic

number) with different mass numbers

Isotopes of chlorine

35Cl 37Cl17 17

chlorine - 35 chlorine - 37

Isotopes of Hydrogen element

H

H

H

11

21

31

has the biggest abundance in nature.

Learning Check 1

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30 2) 35 3) 65

B. Number of neutrons in the zinc atom

1) 30 2) 35 3) 65

C. What is the mass number of a zinc isotope

with 37 neutrons?

1) 37 2) 65 3) 67

Solution

An atom of zinc has a mass number of 65.

A. Number of protons in the zinc atom

1) 30

B. Number of neutrons in the zinc atom

2) 35

C. What is the mass number of a zinc isotope

with 37 neutrons?

3) 67

Learning Check 2

Write the atomic symbols for atoms with the following:

A. 8 p+, 8 n, 8 e- ___________

B. 17p+, 20n, 17e- ___________

C. 47p+, 60 n, 47 e- ___________

Solution

16OA. 8 p+, 8 n, 8 e- 8

B. 17p+, 20n, 17e- 37Cl 17

C. 47p+, 60 n, 47 e- 107Ag 47

Learning Check 3

An atom has 14 protons and 20 neutrons.A. Its atomic number is

1) 14 2) 16 3) 34

B. Its mass number is1) 14 2) 16 3) 34

C. The element is1) Si 2) Ca 3) Se

D. Another isotope of this element is

1) 34X 2) 34X 3) 36X 16 14 14

Solution

An atom has 14 protons and 20 neutrons.A. It has atomic number

1) 14

B. It has a mass number of3) 34

C. The element is1) Si

D. Another isotope of this element would be

3) 36X 14