Structure of the Atom – Atomic Facts

Ch 03 notes

Structure of the atomThe atom has TWO main parts:

1. Nucleus

2. Electron CloudAtoms are electrically neutral

A. Overall charge of an atom is ZEROB. electrons = protons

The Nucleus• Central portion of atom • Make up most of the mass of the atom• Contains two subatomic particles• protons – positive charge(+)

• makes the atom unique

• 1.67266 x 10-27 kg

• neutrons –neutral, no charge(0) • this number can change—still have same element

“isotope”

•1.67495 x 10-27 kg

Electron Cloud

• surrounds the nucleus • electrons –negative • mass of the electron is = 9.11 x 10 -

31 kg• Sub-atomic particle involved in

bonding

Atomic Factsatomic number • the number of PROTONS in the

nucleus

Average atomic mass• the average mass of an atom

of this element, expressed in atomic mass units.

oBecause atoms are so small we use an atomic mass unit(u) = to find the mass of one atom

1 amu = 1.66 X 10-

24 g

6 12.0107

C Carbon

Isotopes• Atoms of the same element with a different number of

neutrons.• http://education-portal.com/academy/lesson/isotopes-and-

calculation-of-a-weighted-average.html

Average atomic mass is a weighted average of these isotopes

• Isotopes have a different mass number but identical atomic number

• The MOST COMMON isotope is represented on the PTE!!!

• https://www.youtube.com/watch?v=pV822HfqT44

Writing Isotopes

Br8135

Bromine-79

Bromine-81

http://www.webelements.com/isotopes.html

More EX: Oxygen, Boron,

Atomic Factso Mass number – number of

protons + neutrons in the nucleus---whole number

o IF NOT GIVEN: Round avg. atomic mass to nearest whole number.

Mass number – atomic number =

neutrons• The number of protons = the

number of electrons– atoms are electrically neutral

8 15.999

O Oxygen

Oxygen-16

Cl

35.45317

Chlorine

Isotopes of Chlorine: Chlorine-35 and Clorine-37Isotopes of Bromine: Bromine-79 and Bromine-81

http://education-portal.com/academy/lesson/isotopes-and-calculation-of-a-weighted-average.html

35 79.904

BrBromine

https://www.youtube.com/watch?v=pV822HfqT44

Calculating Average Atomic Mass

What you need: Percent (%) abundance of each isotope in decimal form

Mass( in amu’s) of each isotope of the element

How to calculate the weighted average by:

1.(mass isotope 1) • (percent abundance in decimal form)=

2.(mass isotope 2) •( percent abundance in decimal form)=

3.(mass isotope 3)• ( percent abundance in decimal form)=

ADD ALL TOGETHER!!!

Calculate the Average Atomic Mass

Mass of Isotope Abundance

24.0 amu 78.70%

25.0 amu 10.13%

26.0 amu 11.17%

Calculate the average atomic mass. What element is this?

Calculate the Average Atomic Mass

• A certain element is a soft, silvery-white metal that has two common isotopes, the first isotope has a mass of 85.0 amu’s the second isotope has a mass of 87.0 amu’s .

• If the abundance the first isotope is 72.2% and the abundance of the second isotope is 27.8%, what is the average atomic mass of this element? What is the element?

Atomic FactsChemical symbols – the abbreviated way to write the

name of an element– a capital letter– cap letter AND lower case letter. – Others come from their Latin name ( Argentum

Ag : silver)

Co vs. COMetal that forms bright

blue solid compounds.

Poisonous gas