Virtually everything that is, is made up of atoms.

Atomic Structure

Chapter 12, page 361

Balloon and sweeter animation

Sub-Particles in the Atom

Each element is chemically unique. To understand why they are unique, you need to know the structure of the atom (the smallest particle of an element) and the characteristics of its components.

Element = made of one kind of Atom. Li

Compounds = made of different atoms chemically bonded in whole number ratios.

H2O•Mixtures are physical combinations of elements or compounds with variable composition

O2 + H2.

Particles or Pure substances

Sub-Particle Mass Charge Locationin the Atom

proton ~1 a.m.u. 1+ in nucleus

neutron ~1 a.m.u. 0 in nucleus

electron ~0 a.m.u. 1- orbits nucleus

Sub-Particles in the Atom

atomic.mass.unit= a.m.u. ~ 1.992 ×10−27 kg or 1/12 the mass of C-12

Size of an atom

• Atoms are incredibly tiny.• Measured in picometers (10-12 meters)

– Hydrogen atom, 32 pm radius• Nucleus tiny compared to atom

– Radius of the nucleus near 10-15 m.– Density near 1014 g/cm3

• IF the atom was the size of a stadium, the nucleus would be the size of a marble.

California WEB

Balloon and sweeter animation

What holds an atom together?

• Nuclear Tug-Of-War• • Electrostatic force – like charges repel and un-like charges

attract

• Strong Nuclear Force – holds nucleons (p+ & n0)• together, very strong nuclear force but over short distances

– Stable nuclei are SMALL– Large nuclei tend to be unstable (radioactive)

• • Electrostatic Force• – Holds electrons on atom

Counting Particles in Atoms

Atomic Number = number of protons (p+) = unique for each element

Atomic Mass Number = Mass of an atom =number of protons + neutrons = (p+) + (no); (e- do not have mass)

California WEB

126C 14

6C

126C

Mass Number = A

Atomic Number = Z

How can I remember how many protons or electrons there are?Just remember the A.P.E. rules!

•atomic number =

•number of protons =

•number of electrons

A

P

E

Now, how do I remember how many protons there are?

Just remember the M.A.N.!•mass number -

•Atomic number =

•number of neutrons

M

A

N

Neon

Ne

Protons:

Electrons:

Neutrons:

Atomic Number: 10

Atomic Mass: 20

10

10

10

Phosphorus

P

Protons: 15

Electrons:

Neutrons: 16

Atomic Number:

Atomic Mass:

15

15

31

Aluminum

Al

Protons:

Electrons: 13

Neutrons: 14

Atomic Number:

Atomic Mass:

13

13

27

Argon

Ar

Protons: 18

Electrons:

Neutrons:

Atomic Number:

Atomic Mass: 40

18

18

22

Silicon

Si

Protons:

Electrons:

Neutrons: 14

Atomic Number: 14

Atomic Mass:

14

14

28

Symbols

Contain the symbol of the element, the mass number and the atomic number (top heavy)

X Massnumber

Atomicnumber

# protons

# protons + # neutrons mass number

Symbols

• Find the – Atomic number– Mass number– number of electrons– number of protons– number of neutrons

F19 9

= 9

= 10

= 9

= 9

= 19

+

So let’s practice!

Symbols

Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass number

Br8035

= 35

= 45

= 35

= 35

= 80

http://www.chem.purdue.edu/gchelp/liquids/bromine.gif

Symbols

Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass number

Na2311

Sodium atom

= 11

= 12

= 11

= 11

= 23

To find net charge on an atom, consider the p+ and the e–.

cation: a (+) ion-- more p+ than e–

-- formed when atoms lose e–

anion: a (–) ion -- more e– than p+ atoms -- formed when gain e–

ion: a charged atom

- -+++- -+

++

-

-

e-

p+

n0

-

+ + +

-+3 and -4 = -1

- - e-

p+

n0

-

+ + +

-+3 and -2 = +1

Ions

Symbols

Find the – number of protons– number of neutrons– number of electrons– Atomic number– Mass number

Na2311

1+

Sodium ion

= 11

= 12

= 10

= 11

= 23

Look

Symbols

If an element has an atomic number of 23 and a mass number of 51 what is the – number of protons– number of neutrons– number of electrons– Complete symbol

V5123

= 23

= 28

= 23

Symbols

If an element has 60 protons and 84 neutrons what is the – Atomic number– Mass number– number of electrons– Complete symbol

Nd14460

= 60

= 144

= 60

Symbols

If a neutral atom of an element has 78 electrons and 117 neutrons what is the – Atomic number– Mass number– number of protons– Complete symbol

Pt19578

= 78

= 195

= 78

Mass Number

• mass number= protons + neutrons

• always a whole number• NOT on the

Periodic Table!

+

+

+

+

+

+

NucleusElectrons

Nucleus

Neutron

Proton

Carbon-12Neutrons 6Protons 6Electrons 6

e-

e-

e-

e-

e-

e-

Isotopes

• Atoms of the same element with different mass numbers.

Mass #

Atomic #

• Nuclear symbol:

• Hyphen notation: carbon-12Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

12

6 C

Isotopes

• Dalton was wrong.• Atoms of the same element can have different

numbers of neutrons.• different mass numbers.• called isotopes.

Isotopes

+

+

+

+

+

+

NucleusElectrons

Nucleus

Neutron

Proton

Carbon-12Neutrons 6Protons 6Electrons 6

Nucleus

Electrons

Carbon-14Neutrons 8Protons 6Electrons 6

+

+

+

+

+

+

Nucleus

NeutronProton

What is an isotope?same number of protons, different numbers of neutrons.

Boron-10

B

Protons:

Electrons:

Neutrons:

Atomic Number: 5

Atomic Mass:10

Boron-11

B

Protons:

Electrons:

Neutrons:

Atomic Number: 5

Atomic Mass:11

5

5

5

5

5

6

B-10

10B 5

B-11

11B 5

Carbon-

C

Protons:

Electrons:

Neutrons: 6

Atomic Number: 6

Atomic Mass:

What is the average atomic mass of Carbon?

Carbon-

C

Protons: 6

Electrons:

Neutrons:

Atomic Number:

Atomic Mass:14

6

6

12

6

8

6

12 14

Isotopes

• Chlorine-37– atomic #:

– mass #:

– # of protons:

– # of electrons:

– # of neutrons:

17

37

17

17

20

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Cl17

37

37

17 Cl

Writing Isotopes• Put the mass number after the name of the

element• carbon- 12• carbon -14• uranium-235

– Or

California WEB

12

6 CMass #

Atomic #

12

6 C

Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart:

Element Symbol AtomicNumber

Mass#

# of protons

# of neutron

# of electron

charge

8 8 8

Potassium 39 +1

Br 45 -1

30 65 30

Atomic Number = Number of Protons

Number of Protons + Number of Neutrons = Atomic Mass

Atom (no charge) : Protons = Electrons

Ion (cation) : Protons > Electrons Ion (anion) : Electrons > Protons

Using a periodic table and what you know about atomic number, mass, isotopes, and electrons, fill in the chart:

Element Symbol AtomicNumber

Mass#

# of protons

# of neutron

# of electron

charge

8 8 8

Potassium 39 +1

Br 45 -1

30 65 30

Oxygen

Bromine

Zinc

O

K

Zn

8

19

35

16

80

19

35

30

20

35

18

36

0

0

Atomic Number = Number of Protons

Number of Protons + Number of Neutrons = Atomic Mass

Atom (no charge) : Protons = Electrons

Ion (cation) : Protons > Electrons Ion (anion) : Electrons > Protons

A N S W E R K E Y

Isotopes

• Because of the existence of isotopes, the mass of a collection of atoms has an average value.

• Average mass = ATOMIC WEIGHT = ATOMIC MASS

• Boron is 20% B-10 and 80% B-11. – That is, B-11 is 80 percent abundant on earth.

• For boron atomic mass= 0.20 (10 amu) + 0.80 (11 amu) = 10.8 amu

Average Atomic Mass

• massed average of all isotopes on the Periodic Table

• round to 2 decimal places

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Avg.AtomicMass

= (mass)(%) + (mass)(%)

100

Average Atomic Mass

• EX: Calculate the avg. atomic mass of oxygen if its abundance in nature is 99.76% O-16, 0.04% O-17, and 0.20% O-18.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Avg.AtomicMass

= (16)(99.76) + (17)(0.04) + (18)(0.20)

100= 16.00

amu

Average Atomic Mass• EX: Find chlorine’s average atomic mass if approximately 8

of every 10 atoms are chlorine-35 and 2 are chlorine-37.

Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem

Avg.AtomicMass

= (35)(8) + (37)(2)

10= 35.40 amu

• Assume you have only two atoms of chlorine.• One atom has a mass of 35 amu (Cl-35)• The other atom has a mass of 36 amu (Cl-36)

• What is the average mass of these two isotopes?35.5 amu

• Looking at the average atomic mass printed on the periodic table...approximately what percentage is Cl-35 and Cl-36?

55% Cl-35 and 45% Cl-36 is a good approximation

Cl35.453

17