Structure of the Atom

SC Standards Covered• Standard PS-2.1 Compare the subatomic

particles (protons, neutrons, electrons) of an atom with regard to mass, location, and charge, and explain how these particles affect the properties of an atom (including identity, mass, volume, and reactivity).

• Standard PS-2.4 Use the atomic number and the mass number to calculate the number of protons, neutrons, and/or electrons for a given isotope of an element.

Scientific Shorthand

• Each element can be represented by a one, two, or three letter chemical symbol

• Each symbol consists of one capital letter plus one or two lower case letters

Atomic Components

AtomAtom - smallest particle of an element which retains the properties of that element.

Atomic Theory

Atoms are building blocks of elements

Similar atoms in each element

Different from atoms of other elements

Two or more different atoms bond in simple

ratios to form compounds

Basic Structure• The center of the atom is called the nucleus.

• Surrounding the nucleus is the electron cloud.

Particle Symbol Location Charge Mass

Electron e-1 Space around the nucleus

-11/1840

amu

Proton

n0

In the nucleus +1

1 amuNeutron

p+1

In the nucleus

0

1 amu

Subatomic Particles

Quarks• Quarks – particles

that make up protons and neutrons

–Three quarks make up a proton or neutron

Fine Points to the Structure of the Atom

• All of the mass of an atom is located in the nucleus

• All of the volume of the atom is taken up by the electron cloud

Atomic NumberAtomic Number

Atomic number – counts the number of protons in an atom

- Used to identify the element- Periodic Table arranged by it

Atoms are electrically neutral (not charged)

# of protons = # of electrons

Learning Check

State the number of protons for atoms of each of the following:

A. Nitrogen

1) 5 protons 2) 7 protons 3) 14 protons

B. Sulfur

1) 32 protons 2) 16 protons 3) 6 protons

C. Barium

1) 137 protons 2) 81 protons 3) 56 protons

Solution

State the number of protons for atoms of each of the following:

A. Nitrogen

2) 7 protons

B. Sulfur

2) 16 protons

C. Barium

3) 56 protons

Mass Number

Mass Number – Counts the number of protons and neutrons in an atom

Number of Neutrons = Mass Number – Proton Number (atomic

#)

What is the Mass Number of the following Atoms?

Isotopes

Isotopes - atoms of the same element with different numbers of neutrons

More Examples of Isotopes

Notation of IsotopesNotation of Isotopes

Potassium - 40

K4019

Mass number

Atomic number

Learning Check

Naturally occurring carbon consists of three isotopes, 12C, 13C, and 14C. State the number of protons, neutrons, and electrons in each of these carbon atoms.

12C 13C 14C 6 6 6

#P _______ _______ _______

#N _______ _______ _______

#E _______ _______ _______

Carbon - 12 Carbon - 13 Carbon - 14

Atomic mass - weighted average of all the isotopes of a particular element

–This is the mass indicated on the periodic table.

–This number will be closest to the most common isotope of the element.

Learning Check

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

Write the isotope (nuclear) notation 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