1. Atomic Structure Nucleus Electron Cloud
Nucleus: contains the protons and neutrons
Nucleus
Electron Cloud
Electron cloud:
A simple atomic model

2. Subatomic Particles what’s inside an atom?
Particle Name Location Charge Mass
Proton (p+) nucleus amu
Electron (e-) cloud x smaller
than p+
Neutron (n0) nucleus amu
Atoms are always neutral because the # protons = # electrons. So + equals -

3. The Nucleus – Pt. 1
Very small, very dense – large mass in a very small volume
Positive charge
Protons and neutrons (nucleons)
Center of the atom
All the atom’s mass is concentrated in the nucleus (the nucleons)

4. The Nucleus – Pt. 2 Nucleons = the particles inside the nucleus and their importance
Protons (p+)
Positive charge
Mass = 1 amu
Atomic number (Z): identifies each unique atom and = the protons
Ex C 92U
Atomic mass (A): mass of atom = p+ + no
Neutron (no)
No charge, neutral
Mass = 1 amu (same as proton)
Atomic mass (A): mass of atom = p+ + no
Ex.

5. Electron Cloud
All electrons are located in the cloud; cloud has a large volume with very tiny mass (low density)
Cloud is negative in charge (because electrons are negative) but…
Atoms are neutral: electrons in cloud = protons in nucleus
Electrons = properties (ex. color, whether it’s a metal, how does it react)
Cloud is built up in layers with each bigger layer able to hold more electrons than the inner ones. The most important layer is the ….
VALENCE SHELL - found on the outer edge of the cloud. Holds the electrons that give the atom its properties. Every element in a FAMILY has the same number of VALENCE electrons

6. Who is this atom and how do you know? Write the correct symbol for it.
Electron layers within the cloud

8. Metals Metalloids (Semimetals) Nonmetals
Lose e- Gain e-
Except:Family 8 has the OCTETand never gains e-

9. ISOTOPES Isotope = different forms of the same atom
How are they the same?
same protons
Same atomic number (Z)
same symbol
How are they different?
different atomic mass (A)
different number of neutrons
Isotopes are like different features on the same model car
different atomic mass
same symbol/atomic number

10. 3 Isotopes of Hydrogen p+ ______ ______ ______ e- ______ ______ ______

11. Isotope Practice #1 p+ ______ ______ ______ e- ______ ______ ______
Determine the number of neutrons in each isotope
p+ ______ ______ ______
e- ______ ______ ______
n0 ______ ______ ______

12. Isotope Practice #2
Using the protons and neutrons, calculate the mass and write the symbol for each isotope:
86 protons and 136 neutrons
7 protons and 8 neutrons
27 protons and 32 neutrons

13. Isotope Practice #3
One last way to identify an isotope is by using its name and its mass (since every isotope is different by mass)
Example: Phosphorus – 31 (or P - 31)
A. Identify these isotopes in this fashion:
12 protons and 12 neutrons protons and 28 neutrons
B. How many protons and neutrons are in each isotope?
Sr – 88 I – Hg - 201

14. Calculating Average Atomic Masses
Use all isotopes to determine the average
Add up all the masses and divide by the total number of isotopes present in the sample
If there are many isotopes – sort them out first
Frequency (Mass #1) + Frequency (Mass #2) …
Total number of isotopes in sample
Frequency is how many times that isotope is counted
… means there could be more than 2 isotopes in the sample

15. Example: calculating average atomic mass
A sample of Ca isotopes:
24(40) + 3(38) + 5(39) + 2(41) 34 34
1351 34
Average atomic mass = amu

16. IONS – How the electron cloud changes
Electron clouds change size when electrons are gained or lost. The atom is no longer neutral and becomes an ION which is either positive or negative
CATIONS are Positive IONS and have lost electrons: Na+1 (Sodium has lost 1 electron)
ANIONS are Negative IONS and have gained extra electrons: P-3 (Phosphorus has gained 3 electrons)
Anion’s names always end in “ide” - ex. phosphide
Electrons removed from or put into the VALENCE SHELL - the outermost part of the cloud
Just remember though, the ion’s symbol hasn’t changed because protons haven’t changed
An ION’S charge = protons - electrons

17. Cations lose electrons = form positive ions = empty the valence shell of the cloud to reach the octet (8).
Sodium atoms have 11 electrons: 1 shell – 2 electrons
2 shell – 8 electrons
3 shell – 1 electron
Na atom
Sodium ion loses 1 electron (it’s in Family 1) and forms a +1 ion. Notice the 3 shell is now empty, but the 2 shell has the octet (8).
Na+1 ion

18. Anions gain electrons = form negative ions = finish filling the valence shell of the cloud to reach the octet (8).
Chlorine atoms have 17 electrons: 1 shell – 2 electrons
2 shell – 8 electrons
3 shell – 7 electron
Chlorine ion gains 1 electron (it’s in Family 7) and forms a -1 ion. Notice the 3 shell is full and has the octet (8).

19. X Atomic mass (p+ + no) Element Symbol Ion Charge (p+ - e-) A charge Z
subscript
Atomic number
(protons)
Subscript (in compounds only)

20. Comparing Atoms, Isotopes, and Ions

21. Radioactivity
Breakup of an isotope’s large unstable nucleus into a smaller more stable isotope nucleus (decay)
Some isotopes are radioactive, some aren’t
Why is the nucleus unstable?
Neutron to proton ratio: Most stable atoms have 1:1 no to p+ ratio. Last stable ratio is 1.51:1 no to p+ ratio (206Pb)
Strong nuclear forces (the “glue” that holds the protons to the neutrons) can’t hold nucleus together

22. Radioactivity – Pt. 2
Radiation: particles and energy released from a nucleus during its decay
Transmutation: original nucleus changes into a new nucleus with a different mass and/or identity
Half-life: time required for half the atoms of a radioactive isotope to decay into something smaller and more stable (or less radioactive)
To do this, the radioactive nucleus releases radiation

23. Types of Radiation Alpha Particle () Helium nucleus
Massive particle; common for heavy radioactive isotopes to release these
When released changes both identity and mass
Slow; easy to block with paper, Al foil, plastic
Used in smoke detectors

24. Types of Radiation 2) Beta Particle (β) A high speed electron
Faster than an alpha particle because it’s so tiny
When released, changes the identity but not the mass
Passes 1-2 cm deep into the skin and can damage it
Can pass through paper but is blocked by Al foil

25. Types of Radiation 3) Gamma Rays (γ ) Not a particle but pure energy
Fastest of all radiation types and most dangerous
Blocked by lead shields

26. Types of Radiation Radioactive isotopes can also release:
4. Proton particles
Will change mass and identity
5. Neutron particles
Will change mass only

27. Transmutations, Fission, and Fusion (nuclear Equations)
The change of one radioactive element and its nucleus into another (mutation)
Done by releasing radiation (alpha, beta, protons, or neutron release)
Done by absorbing radiation or other small atoms (fusion). So 2 nuclei join together to produce something bigger
Done by collisions between large radioactive atoms and smaller atoms. Result is the large atoms breaks apart (fission) in a chain reaction

28. Nuclear Equations Pt. 2
In all nuclear equations (radiation release, fission, and fusion), total mass (A) and total identity (Z) are conserved.
Original radioactive atoms  Final radioactive atoms
Ex. Radioactive Polonium-222 releases beta radiation.
Check A and Z:
222 =
and
Z) =
New radioactive atom
Beta particle radiation
Original radioactive atom
releases or equals

29. Half - Life
Half-life: time required for half the atoms of a radioactive isotope to decay
Some isotopes have long half-lives, some are short.
Ex. U-238 has a half life of 4.46 x 109 years and Co-60 has a half life of 10.5 minutes
After 1 decay, half of the isotope’s atoms are still radioactive and half are now stable (or less radioactive and not the same isotope at the start)

30. How to solve Half-life problems
To calculate the number of decays use:
total decay time
half-life
To calculate the half-life use:
total decay time
number of decays
Decays
Half –life or time passed
% or amount left
Put your starting amount here
Set up your grid. The number of columns changes from problem to problem

31. With each C-14 half-life that passes, (5760 years) the % goes down by ½, and the years go up by 5760
Decays 1 2 3 4 5
Years passed
5760
11520
17280
23040
28800
% radioactive
100 50 25
12.5
6.25
3.125

32. Half-Life Practice Problem
Radioactive Oxygen-19 has a half-life of 27 seconds. If a laboratory has a sample of 40 atoms of Oxygen-19, how many does it have left after 108 seconds?
Step 1: Calculate the number of decays (columns) to put in your grid
Total time = 108 seconds = 4 decays
half-life 27 seconds
Decays 1 2 3 4
Half-Life Time passed
seconds 54 81
108
135
Amount of
atoms 40 20 10 5
2.50
Step 2: Set up your grid with 4 columns and fill in the boxes.

33. Areas of Guided Notes Left Blank Earlier in Presentation
5B Complete the VALENCE SHELL diagrams for each of the families of Periodic Table.
When the elements combine they can either share or exchange valence electrons, to reach the perfect number, or octet (8) just like Family Noble Gases the family that already has a complete valence shell

34. 26. The electron cloud changes sizes when the electrons are lost or gained. When this happens, the atom is no longer NEUTRAL and is called an ION.
27. Ions form when atoms want to have a complete valence shell. A valence shell is complete when it has 8 electrons, or an octet. Family 8 (Noble Gases) is the only family on the periodic table with a complete valance shell
33. The charge of an ion is always shown in the exponent to the right of the ion’s symbol.

35. 34. METALSform cations (+ ions) and are found on the LEFT side of the periodic table.
35. In general, the LARGER the atom and its cloud, the easier it is for it to lose electrons and form a cation (+ ion).
NON METALS form anions (- ions) and are found on the RIGHT side of the periodic table.
In general, the SMALLER the atom and its cloud the easier it is for the cloud to gain electrons and form and anion (- ion).

36. Family 8 (Noble Gases) doesn’t ever form ions because it already possesses a full valence shell or 8 valence electrons. This means this family never forms compounds.

37. Eample: Radioactive Radon 222 releases alpha radiation
Rn He Po
H + H He n

38. Number of Decays 1 2 3 4 5 6
Half Life
8 minutes 16 24 32 40 48
% Remaining
100 50 25
12.5
6.25
3.125
1.5625
Number of Decays 1 2 3 4
Half Life
4.7 years
9.4
14.1
18.8
% Remaining
100 50 25
12.5
6.25