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Standards 1a. Students know how to relate the position of an

element in the periodic table to its atomic number

and atomic mass. 1b. Students know how to use the periodic table to

identify metals, semi-metals {metalloids}, non-metals, and halogens

1e. Students know the nucleus of the atom is muchsmaller than the atom yet contains most of itsmass.



Objectives Know the 3 particles of the atom and where they

reside

Know the difference between atomic number andmass number

Know how to write nuclide symbols

Know the three isotopes of hydrogen

Know how to calculate atomic mass

Know how to calculate percent composition



First Some Questions… What are atoms made up of?

Protons, Neutrons and Electrons

Where do you find these particles? Protons and Neutrons are located in the nucleus

Electrons are located in the outer rings, outside thenucleus.



Vocabulary Atom- from the Greek atomos=indivisible. The atom is the

smallest particle of an element that retains the propertiesof that element.

Nucleus: the center of the atom; composed of neutronsand protons. Because the mass of the proton and theneutron is much larger than that of electrons, almost allthe mass is located in the nucleus.

Ion: a charged particle; # protons ≠ # electrons

Electrons occupy most of the volume of an atomoutside/around the nucleus.



Fundamental Particles Proton

A positively charged particle located in the nucleus.

Neutron A neutral particle located in the nucleus.

Electron A negatively charged particle located outside the

nucleus.



Question What differentiates one atom from another atom?

The number of PROTONS



Atomic Number (Z) Number of protons in the nucleus of an atom

This number is found on the Periodic Table

Atomic Number identifies an element Always a positive number (b/c it is a counting

#)

Tells number of electrons in a neutral atom

An atom is electrically neutral

El A

Z



What does it mean to be

electrically neutral? The atom has no charge

The number of protons = the number of electrons



Question What observations can you make about atomic

numbers on the periodic table?

Atomic Number increases as you go across the rows fromleft to right.



Questions What is the atomic number of Chlorine?

What can you tell me about its protons and electrons?

What element has 20 protons? What is the relationship between the # protons and

the atomic number?

They’re equal.



Complete the Chart

Element Symbol Atomic # # Protons

Potassium

5

16

Y

K 19 19

Boron B 5

Sulfur S 16

Yttrium 39 39



Mass Number (A)

Total number of protons and neutrons in thenucleus of an atom

Always a positive number You can determine the nuclear composition

of an atom from its mass number and atomicnumber

El A

Z



Question What do the atomic number and the mass number

have in common?

Both Positive integers

Both have the same # of protons



How to find # of Neutrons Mass # - Atomic#= # Neutrons

Or

# protons + # neutrons= Mass #

(atomic number + # neutrons)=Mass #



Complete the Chart

Atomic# Mass# #Protons #Neutrons #Electrons Chemical

Symbol

9 10

14 15

47 22

55 25

6 C

19 9 9 F

14 29 14 Si

22 22 25 Ti

25 30 25 Mn

6 12 6 6



Isotopes Atoms of the same element with differing numbers of

neutrons

Atoms with the same atomic number but different

mass number Isotopes of an element have different masses

Chemical properties of different isotopes are virtually the same



Nuclide Symbol

A=Mass # Z= Atomic #

El

A

Z



Nuclide A specific kind of atom

Specification of an element in terms of itsnuclear composition/structure

Tells number of protons and number of neutrons

# protons # neutrons # electrons Chemical

Symbol

C 6 [6, 7, 8] 6

Nuclide Symbol 6 7 6 C 13

6



Complete the Chart Atomic# Mass# #Protons #Neutrons #Electrons Chemical

Symbol

9 10

14 15

47 22

55 25

6 C

19 9 9 F

14 29 14 Si

22 22 25 Ti

25 30 25 Mn

6 12 6 6

NuclideSymbol

F

19

9

Si29

14

Ti47

22

Mn55

25

C 12

6



3 Isotopes of Hydrogen

Isotope

Of Hydrogen

Nuclide

Symbol # protons # neutrons # electrons

H 1

1

H 3

1

H 21Deuterium 1 1 1

Protium 1 0 1

Tritium 1 2 1



Nuclides By specifying the nuclear structure, then you call it a

nuclide. But if you say Carbon atom, you do not know which

Carbon atom it is, therefore you don’t know how many neutrons it has

Example: Brothers and Sisters- You are members of the Jones family, but you have not

specified which Jones member you are referring to.



Write the nuclide name and nuclide symbol

# protons # neutrons # electrons NuclideName

NuclideSymbol

17 20 18

20 20 18

92 146 92

Chlorine-37 Anion

Cl 37

17

240

20Ca

U 238

92

Calcium-40Cation

Uranium-238



Atomic Mass A weighted average of the atoms in a naturally

occurring sample of the element.

Naturally occurring: no matter where you get the samplefrom, it will have the same percentages of isotopes.



Construct a Fruit Basket Fruit Type Weight of Each Piece

2 grapefruit 14 oz

4 apples 10 oz3 pears 7 oz

1 kiwi 3 oz

What is the Average Weight?



Fruit Basket Average weight=9.2oz

Each type of fruit makes a different contribution to theoverall weight

How many pieces of fruit actually weigh 9.2 ounces? None!

What does 9.2 oz mean? Fictitious non-existent piece of fruit



Atomic Mass If you have a recipe, you could count items to put

in, say 200 chocolate chips, 3 eggs, etc.

But suppose I have a recipe to make a compound. I need 100 hydrogen atoms and 50 oxygen atoms-you

cannot count atoms or pluck them out with atomictweezers!

So instead they mass them (weigh them) Careful here, the mass of an object is completley

different from the weight of an object.



Question What accounts for the mass of the atom?

# protons & # neutrons in the nucleus



Atomic Mass

Know that 1.0 amu is defined as exactly 1/12the mass of a atom.

Carbon-12 has 6 protons and 6 neutrons,therefore 1 proton or 1 neutron = ~1 amu

1 amu = 1.6606 x 10 -24 grams

Since the mass mostly depends on # protons

and # neutrons, you’d think atomic mass would be a whole number, but it isn’t. How come?

C 12

6



Atomic Mass In nature, most elements exist as a mixture of 2 or more isotopes. Each isotope of an element has a fixed, constant mass and fixed constant

relative abundance.

Relative abundance-

(amount) X 100= %(how much of each isotope is present)

Sample of carbon from anywhere in the world; coal from S. Africa, W. Virginia or Pennsylvania → 99% C-12 and 1% C-13

Atomic Mass of periodic table takes into account the larger and smaller

masses of the isotopes, just like the average piece of fruitaccommodated the larger and smaller masses. → Idea of weighted average



Calculating Atomic Mass To calculate atomic mass you need to know 3 things:

# of stable isotopes

Mass of each isotope

% abundance of each isotope Each isotope is a piece of fruit and the isotope’s mass is

the weight of each piece of fruit.



Example: Chlorine Calculation

mass of isotope X relative abundance

+ mass of isotope X relative abundance=_______amu

(34.969)(.7553) + (36.935)(.2447) =

That’s the same value on the periodic table!

Isotope Mass of Isotope Relative Abundance Atomic Mass

Cl-35 34.969 75.77%

Cl-37 36.935 24.23%

35.4500amu



Question How many chlorine atoms actually have a mass of

35.45 amu?

NONE

So the atomic mass, in amu, is the average of afictitious non-existent atom of an element.



Example: Copper CalculationIsotope Mass of Isotope Relative Abundance Atomic Mass Cu-63 62.9298amu 69.09%

Cu-65 64.9278 30.91%

(62.9298)(.6909)+(64.9278)(.3091)= 63.5464 amu



Calculating Relative Abundance To Calculate % Abundance:

Make a Chart

Isotopic Mass X %Abundance of each isotope Set-up equation

Solve for “x”

Plug in “x” value to solve for “y”



ExampleIsotope Mass of Isotope Relative Abundance Atomic Mass B-10 10.013

B-11 11.009

1.00x + y = 1.00y = 1 – x

10.103 (x) + 11.009 (1 –x) = 10.811

10.103x + 11.009 -11.009x = 10.811

-0.996x = -0.198

x = .1987

y= 1-.1987 y= .8013

B-10 = 19.87%

B-11 = 80.13%

x

1- x



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