Atoms & Elements

•What is an atom?

An atom is the smallest particle of an element that retains its identity in a chemical reaction.

Word origin: atom comes from the Greek word atomos meaning “ indivisible”

•Elements & Compounds

• What would atoms of an element, mixture and compound look like at a microscopic level?

• The parts that make up an atom!• protons • neutrons• electrons

•Subatomic Particles

nucleus

proton

neutron

electron

• Found in the nucleus

• Identifies the element

• #of protons = specific element

• Responsible for chemical and physical properties

• Found in the nucleus

• Plays no role in chemical behavior

• Purpose: to put space between protons

• Spin around in set regions outside of nucleus

• Most important in chemical reactions

• Farthest electron away from nucleus determines how atoms chemical to combine to one another.

•Subatomic ParticlesElectronsNeutronsProtons

Name Symbol Charge Relative Mass

Proton p+ +1 1

Neutron no 0 1

Electron e- -1 0 (1/1840)

•Subatomic Particles

How big is an atom?

Imagine the nucleus is the size of a marble located in the middle of the football field,

the electron would be in the classroom the size of a period!

•Periodic TableGreatest Cheat Sheet Ever!

• Rows: periods• 7 periods

• Columns: groups or families• 18 Groups

• 1A: Alkali Metals• 2A: Alkaline Earth Metals• 7A: Halogens• 8A: Noble gases• B Groups: Transition and Inner

Transition Metals

•Periodic Table Categories:MetalsNonmetalsMetalloids(B, Si, Ge, As, Sb, Te, At)

•Periodic Table

14

SiSilicon28.086

Atomic Number

Symbol

Element name

Atomic Mass

• Counts the number of protons in an atom within the nucleus

•Atomic Number• Important Numbers

14

SiAtomic Number = # of protons

Silicon has 14 protons

•A. Nitrogen•B. Potassium•C. Neon

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

•Atomic Number

•A. Nitrogen• 7 protons

•B. Potassium• 19 protons

•C. Neon• 10 protons

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

•Atomic Number

•An atom is neutral•The net charge is zero•Number of protons = Number of electrons•Atomic number = Number of electrons•Remember: proton = +1 electron = -1

•Number of Electrons

•Number of Electrons

14

Si14 protons14 electrons

-14 +14

= 0 neutral

• Counts the number of protons and neutrons in an atom

OR• Determined by: the whole number closest to the Atomic Mass

• Mass Number• Important Numbers

14

SiSilicon28.086 Atomic Mass

• Show the mass number and atomic number• Give the symbol of the element

• Atomic Symbols•Mass Number

2814Si

Mass Number

Atomic Number

silicon-28

•Determine the Mass Numbers

4Be

9.0122

27Co

58.933

10Ne

20.179

9 59 20

•Write the Symbol and Name for each

4Be

9.0122

27Co

58.933

10Ne

20.179

Be94

beryllium-9

5927Co

cobalt-59

2010Ne

neon-20

• The total number of particles in the nucleus• # of protons + # of neutrons

• To determine the number of neutrons• Mass number – Atomic number = # of neutrons

•Mass Number

168

3115

6530

#p

#n

#e

O P Zn

8p+

8no

8e-

15p+

16no

15e-

30p+

35no

30e-

• The atomic number identifies the element, but an element may have atoms with several different mass numbers.• Most elements consist of several different isotopes• Same number of protons , Different number

of neutrons

• Isotopes

3517Cl 37

17 Clchlorine-35 chlorine-

37

• Naturally occurring hydrogen consists of 3 isotopes, protium (H-1), deuterium (H-2), and tritium (H-3). State the number of protons, neutrons, and electrons.

• Isotopes of Hydrogen

11

21

31

#p

#n

#e

H H H

1

0

1

111

1

21

• A. Number of protons

• B. number of neutrons

• C. What is the mass number of a calcium isotope with 19 neutrons?

•An atom of Calcium (Ca-40)

• This is NOT a whole number• A given element can have atoms with several different mass numbers.• Average mass of the atoms with all possible mass numbers• We will calculate later

•Atomic Mass

•A. 11p+, 12no, 11e-

•B. 17p+, 20no, 17e-

•C. 47p+, 60no, 47e-

•Write the atomic symbol

•A. 11p+, 12no, 11e-

•B. 17p+, 20no, 17e-

•C. 47p+, 60no, 47e-

•Write the atomic symbol2311 Na

3717

Cl

10747

Ag

• Remember atoms are neutral, therefore if an atom has a charge we call it an ion.

• Ions- Atoms which gain or lose an electron

• Atoms with a charge (positive or negative)• Ions

atom ion#p 11 11#e 11 10

atom ion#p 17 17#e 17 18

Na1+

Cl1-

Why do the electrons change?

• If protons change…new______?________

• If neutrons change…new______?______

• If electrons change….new _____?______

•Why?

• If protons change…new element• If neutrons change…new isotope• If electrons change….new ion

•Why?

atomion

#p 12 12

#e 12 10

atom ion#p 8 8

#e 8 10

• Ions

Mg 2+

O 2-

• What does each represent? • How many of what subatomic particles does each represent?

•Complete Atomic Symbolcombines isotopes and ions

27

13

Al 3+

•Complete Atomic Symbolcombines isotopes and ions

27

13

Al 3+

13p+ 10e- 14no

Ionic chargeMass number

Atomic number

7p+7no10e-

15p+17no18e-

30p+35no28e-

N3- P3- Zn2+

•How many protons, neutrons, & electrons?

147

3215

6530

Coming back to this…Atomic mass is the weighted average mass of all the atomic masses of the isotopes of that atom.

So we involved all the different forms of ATOMS of an element (ions not an issue here) and how frequent they are

•Atomic Mass

• To find the Average Atomic Mass (generally referred to as the atomic mass of an element) we need to use two things

• The mass of the isotope• Multiplied by its frequency• Then we add all the forms up.

•Average Atomic Mass cont.

Cl-35 is about 75.5 % and Cl-37 about 24.5% of natural chlorine. 35 x 75.5 = 26.4 100

35.5 37 x 24.5 = 9.07

100

•Example of Average Atomic Mass

ADD US UP

•Rubidium has two common isotopes, Rb-85 and Rb-87. If the abundance of Rb-85 is 72.2% and the abundance of Rb-87 is 27.8%, what is the average atomic mass or rubidium?