Atomic StructureChapter 4

Sizing up the Atom O Radii of most atoms: 5 x 10-11 m to 2 x

10-10 mO Copper penny contains 2.4 x 1022

atoms. The population of Earth is about 6 x 109 people. There is about 4 x 1012 times as many atoms in a coin than people on Earth.

O Line up 100,000,000 copper atoms side by side, the line would be only 1 cm long

Subatomic particlesO Proton: positively charged subatomic particle (p+)O Neutron: neutral subatomic particle (n0)O Electron: negatively charged subatomic particle

(e-)O Protons and neutrons are the same size, but

electrons are 1840 times smaller.O *All atoms are neutral*

O Nucleus: tiny central core of an atom and is composed of protons and neutrons with an overall positive charge.

Nuclear AtomO Protons and neutrons are located in

the nucleus (positive charge)O Electrons are distributed around the

nucleus and occupy almost all the volume of the atom (negative charge)

O The positive nucleus is balanced out with equal number or electrons. Atoms are always neutral.

Atomic NumberO Elements are different because they

contain different numbers of protonsO Atomic number: number of protons in

nucleus of atomO All atoms are neutralO # protons = # electronsO Blue number in upper right hand corner for

each element on periodic tableO Nuclear charge is the charge of the nucleus

and is dependent on the number of protons.

Atomic MassO The weighted average mass of atoms in a

naturally occurring sample of the elementO Reflects both the mass and the relative

abundance of the isotopes as they occur in nature

O Isotope: atoms that have same # of protons but different # of neutrons (different mass numbers)

O Neon-20, Neon-21, Neon-22O http://education.jlab.org/itselemental/

iso006.html

Mass NumberO Most of atom’s mass is concentrated

in nucleus and depends on # protons and neutrons

O Mass number: total number of protons and neutrons in nucleus of atom

O # neutrons = mass # – atomic #O To determine the mass # you round

the atomic mass to the nearest whole #

Atomic Mass Unit (AMU)

O 1/12 the mass of a carbon -12 atomO More useful to compare the relative

masses of atoms using a reference isotope as a standard.

O Reference isotope: Carbon-12O Helium mass = 4.00260 amu and is

1/3 the mass of carbon-12O Table 4.3

To calculate atomic mass:

O Multiply the mass of each isotope by its natural abundance, expressed as a decimal, and then add the products.