BUILDING ATOMSAtomic structure

Unit 1 • Investigation III

ChemCatalyst • A Bohr model of a helium atom and a

beryllium atom are given below.

Helium, He Berylium, Be

(cont.)

Unit 1 • Investigation III

a. List three similarities and three differences between the drawings

b. How do you think a gold atom would be represented different from a copper atom?

Compare Helium and Berylium

Differences between Gold and Copper?

Unit 1 • Investigation III

The Big Question

–What does the periodic table tells us about the structures of different atoms?

Unit 1 • Investigation III

BY the end of the section, you should be able to:

1. Use the periodic table to identify the number of:

protons, neutrons, electrons in a neutral element’s atom.

2: Determine what the atomic number represents about the atom

3. Determine the atomic mass of any atom

Opening questions in the lab

1.For each atom shown to be neutral, what must be true about the number of protons and electrons it has?

2.How can you identify the neutrons in the diagrams?

3.List the number of electrons, protons and neutrons for each atom shown

Bohr Models of atoms

Beryllium Atom Fluorine Atom Carbon Atom

Comparison

• Compare the numbers in the periodic table to the pictures of the atoms

• What connections do you see?

HOW DO YOU DETERMINE THE NUMBER OF PROTONS IN AN ATOM?

Atomic number

• Whole number

• Equals the number of protons in a single element atom

Proton changes

• If a proton is added or subtracted to atom, the atom becomes a new element!

Question set 1

• How many protons do Ca, HS, Kr have?

• What element has 48 protons

• If I can add 1 proton to a gold atom, what have I created?

HOW DO YOU DETERMINE THE NUMBER OF ELECTRONS IN AN ATOM?

Determining electrons

• If the atom is neutral, the number of electrons equals the number of protons

# protons = Atomic # = # electrons

Question set 2

• How many electrons does a neutral atom of – Cs– Hg– BrHave?

HOW DO YOU DETERMINE THE ATOMIC MASS OF AN ATOM?

Atomic mass and mass number describe the same thing

Determining the Mass Number of an atom

• Is the mass of an individual atom

• Sum of protons and neutrons in nucleus

• Each proton or neutron has a mass value of 1 atomic unit (1 amu)

• Electrons’ mass are insignificant (why?)

Unit 1 • Investigation III

Since mass value is arbitrarily assigned , could also be used to represent weight

The number on the periodic table represents the average mass (weight) of an individual atom of a specific element

Why is the Atomic weight usually a decimal?

Atomic weight

Answering questions with questions

• Do stable atoms have parts of protons or neutrons?

• Do all atoms of the same element have the same number of protons and neutrons?

Answers

• The Atomic weight is the average weight(mass) of EVERY atom of that element

• Not all atoms are the same• No partial subatomic particles

To determine the mass number of the most common version of an

element

• Round off the weight to the nearest whole number

Question set 3

• If an atom had 23 protons and 24 neutrons, what would be its mass number?

• What is the mass number of the most common version of Vanadium?

• What is the atomic weight of Argon? Its most common mass number?

HOW DO YOU DETERMINE THE # OF NEUTRONS IN AN ATOM?

Determining neutrons

• Subtract the number of protons (represented by the atomic number) from the atomic mass of the atom

• Neutrons = Mass number – Atomic number

Question 4

• What is the number of numbers in the most common version of the following atoms:

• Be

• Rn

• La

In your Comp Book

Draw a Lithium atom with 4 neutrons using the Bohr-orbital style

Check with your neighbors, any variations?

Class/Lab assignment

• Each Person must complete their own chart. Students at table may work together.

• Identify the names of the unknown elements

• You may use a periodic table to help you complete the chart

Unit 1 • Investigation III

element chemical symbol

atomic number

# of protons

# of electrons

# of neutrons

mass number

atomic weight

beryllium 5

fluorine 10

6 12

chlorine 18 35.45

lead 126

potassium 19 39

tin 70

tungsten 184 183.85

29 36

gold 118

“Building atoms” Chart

Questions on the chart?

Conclusions

• Looking at the periodic table:

• What number indicates the amount of protons found in each element’s atom?

• What number used to organize elements on the periodic table?

(each element has a unique value, arranged sequentially)

What would you have to do to turn a copper atom into a gold atom?

Is there a better element to start with than copper? Why?

Unit 1 • Investigation III

Check-In

• Use your periodic table to identify the following elements:

a) Element that has an Atomic number of 18b) Neutral element that has three electronsc) Element that has an Atomic mass of 16.0d) The number of neutrons an atom of Iridium

has is its atomic mass is 192 amu

Unit 1 • Investigation III

Making Sense

– If you know the atomic number of an element, can you figure out how many neutrons an atom of that element has? Can you come up with a close guess? Explain.

Unit 1 • Investigation III

Wrap-Up– Each successive element has one more proton

than the element preceding it.

– The atomic number is equal to the number of protons.

– The atomic mass equals the sum of the number of protons and neutrons in an atom

– The atomic weight is the average mass of all atoms of an element. It is the decimal value found on the periodic table (cont.)

If you finish early…

• Look at Te and I in the periodic table. What is unusual about their numbers in the table

• Are there other examples in the periodic table?

• Why does Iodine (I) not have an atomic weight higher the Te (tellurium)?

WHY ARE THE MASSES OF ALL CARBON ATOMS NOT THE SAME?

The answer

The number of neutrons can vary in atoms of a specific element