Properties of atoms
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1. Properties of Atoms. 2. Atomic Structure Goals. SC3 Students will use the modern atomic theory to explain the characteristics of atoms. a. Discriminate between the relative size, charge, and position of protons, neutrons, and electrons in the atom.

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Properties of Atoms

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Properties of Atoms


Atomic Structure Goals

SC3 Students will use the modern atomic theory to explain the characteristics of atoms.

a. Discriminate between the relative size, charge, and position of protons, neutrons, and electrons in the atom.

b. Use the orbital configuration of neutral atoms to explain its effect on the atom’s chemical properties.

c. Explain the relationship of the proton number to the element’s identity.

d. Explain the relationship of isotopes to the relative abundance of atoms of a particular element.

e. Relate light emission and the movement of electrons to element identification.


This will be our FOCUS







What is an Element?

  • One of the ~116 known “Pure”, un-cutable substances….that still retain the properties of that substance.



What is an Atom?

  • Smallest piece of matter that still retains the properties of that matter.

  • What are they composed of?


Bohr Model- electrons are found only in specific circular paths, or orbits, around the nucleus.

Electron Cloud Model: Probable locations of electrons.


Quantum Mechanical Model: Mathematical model describing the behavior of electrons and energy of electrons in various locations around the nucleus.

Atomic Structure


Subatomic Particles

  • Protons

  • Neutrons

  • Electrons


Atomic Structure



What makes one element different from another element?

Number of protons.

Atomic Structure

Atomic Structure


Rutherford’s Gold Foil experiment led to the discovery of a positive nucleus.

Atomic Structure



  • Positive Charge

  • The number of protons determines which element it is.

  • All elements have different numbers of protons

  • 1 amu

  • Composed of quarks

Atomic Structure


  • Neural charge

  • Located in the nucleus

  • 1 amu

  • Composed of quarks

Atomic Structure



  • Smallest subatomic particle.

  • 1/1800 the mass of a proton.

  • Orbit nucleus.

  • Negative Charge

Atomic Structure


  • Electrons are found in different levels around the nucleus.

  • These are called Energy Levels or shells.

  • Each energy level also has “sublevels” or orbitals

Atomic Structure


Atomic Structure



Electrons are found in the

Electron cloud

surrounding the nucleus.

Atomic Structure


Each Energy Level Can Hold A Certain Number of Electrons!

Only TWO on the first level!

Atomic Structure



Different atoms have different numbers of electrons!

Each Energy Level Can Hold A Certain Numbers of Electrons!

Eight on the 2nd


Atomic Structure


Atomic Structure

Atomic Structure




  • Atomic Number

  • Number of Protons

  • Atomic Mass

  • Sum of Protons & Neutrons


The # of Protons determines the identity of an element. All elements have different number of protons.


How can I find out how many electrons an atom has?

  • Atom= neutral

  • So, the number of protons = electrons.

  • Atomic number tells you the number of protons.................

  • So, it also tells you the number of electrons!

Atomic Structure

  • Practice with a friend…………

Quantum Mechanical Model

  • Based on quantum theory, which says matter also has properties associated with waves.

  • According to quantum theory, it’s impossible to know the exact position and momentum of an electron at the same time. This is known as the Uncertainty Principle.

  • This model of the atom uses complex shapes of orbitals(sometimes called electron clouds)

    • Orbitals: volumes of space in which there is likely to be an electron.

      So, this model is based on probability rather than certainty.

Atomic Orbitals

  • An atomic orbital is a region of space in which there is a high probability of finding an electron.

  • Energy levels of electrons are labeld by principal quantum numbers (n).

  • Each energy sublevel corresponds to an orbital of a different shape, which describes where the electron is likely to be found.

  • Different orbitals have different shapes.


Quantum Numbersn, l, m, s

  • Describing electron locations

  • 4 quantum number.

  • 1st-Principle Quantum # = n

    • Which energy level the e- is in.

    • n= 1-7 (there are only 7 energy levels)

  • Max # formula= 2n2

  • the larger the value of n, the farther away from the nucleus and the higher the energy of the electron.

2nd quantum number= l

  • Describes the shape (orbital)

  • Shapes: s, p, d, f

  • Each shape “sublevel” can only have 2 electrons.

  • Max electrons in each sublevel:

    • s=(1x2)2, p=(3x2)6, d=(5x2)10, f=(7x2)14

# of sublevels

s & p

S (1),p (3), d (5)

# of sublevels (shapes)

F (7)

  • 3rd quantum number= m

    • Describes orientation in space

    • x, y, z

  • 4th quantum number= s

    • Describes the spin of the e in the orbital

    • Clock or counterclock

  • Brain Break

  • Clip


Orbital Filling Diagrams (3 rules)

  • Aufbau Principle: e- occupy orbitals of the lowest energy first.

p.133 text


Orbital Filling Diagrams

  • Hund’s Rule: one electron in each orbital, then electrons pair up with opposite spins.

  • Pauli Exclusion Principal: An orbital may have no more than 2 electrons. 2 e- cannot have the same spin in the same orbital.


  • Practice:

  • H, C, Na, S, Ar, K.

  • We can use the periodic table to predict which sublevel is being filled by a particular element.

Blocks and Sublevels


Electron Configuration Notation

Practice: Write the electron configuration notation.

NameAtomic NumberElectron Configuration

  • Oxygen81s2 2s22p4

  • Aluminum131s2 2s22p63s23p1

  • Chlorine171s2 2s22p63s23p5




Electrons and Light Emission

  • When atoms absorb energy, electrons move into higher energy levels (excited state).

  • When the return to their ground state, the lose energy by emitting light.

  • The light emitted is a mixture of a specific frequencies.


  • A quantum of energy is the amount of energy required to move an electron from on energy level to another energy level.

  • The higher the ground state, the less energy it take to move to a higher energy level.

Electrons & Light Emission

  • Each frequency is a different color.

  • When the frequencies are passed through a prism, the colors are separated & an atomic emission spectrum is created for that element.


  • Larger “jump”- more energy-more towards the blue side

  • Smaller “jump”- less energy-more towards the red side


  • The flame test is used to visually determine the identity of an unknown metal or metalloid ion based on the characteristic color the salt turns the flame of a bunsen burner





Isotopes are atoms that have the same number of protons and differonly in the number of neutrons.

Most isotopes are stable but radioactive isotopes are unstable and break down into more stable forms byemitting particles and energy (radiation).

Radiation can be detected, so radioactive isotopes are useful as labels in scientific research and medical diagnostic procedures.




Let’s Do some practice problems 



  • How do you find this number?



Calculating Average Atomic Mass

  • Percent(%) abundance of isotopes

  • Weighted average= Mass of each isotope x % abundance of that element


Atomic Mass of Magnesium

Isotopes Mass of Isotope Abundance

24Mg =24.0 amu 78.70% = ______

25Mg = 25.0 amu 10.13% = ______

26Mg = 26.0 amu 11.17% = ______

Atomic mass (average mass) Mg = 24.3 amu





  • Gallium is a metallic element found in small lasers used in compact disc players. In a sample of gallium, there is 60.2% of gallium-69 (68.9 amu) atoms and 39.8% of gallium-71 (70.9 amu) atoms. What is the avg. atomic mass of gallium?



  • A sample of boron consists of 10B (mass 10.0 amu) and 11B (mass 11.0 amu). If the average atomic mass of B is 10.8 amu, what is the % abundance of each boron isotope?

Counting Atoms

  • The Mole



The Mole

  • For a given molecule (atom), one mole is a mass (in grams) whose number is equal to the atomic mass of the molecule (atom)

What is the Mole?

A counting number (like a dozen)

Avogadro’s number (NA)

1 mol = 6.02  1023 items


The Mole

  • 1 mole of molecules has a mass equal to the molecular weight in grams.

  • A mole of carbon-12 atoms has a mass of just 12 g.

  • How many Atoms is that???

  • 1 mole = 6.022 x 1023 atoms

  • Amedeo Avogadro (1776-1856)

    Avogadro's number


    Molar Mass

    • Mass of 1 mole of an element or compound.

    • Atomic mass tells the...

      • atomic mass units per atom (amu)

      • grams per mole (g/mol)

        • 1 atom of C = 12.01 amu

        • 1 mol of C = 12.01 g

    • Round to 2 decimal places


    Molar Mass Examples

    • lithium

    • aluminum

    • zinc

    6.94 g/mol

    26.98 g/mol

    65.39 g/mol


    Molar Conversion Examples

    • How many grams of iron are in 2.25 mol of iron?

    2.25 mol Fe

    55.85 g Fe

    1 mol Fe

    = 126 g Fe


    Molar Conversion Examples

    • How many moles of calcium are in 5.0 g of calcium?

    5.0 g Ca

    1 mol Ca

    40.08 g Ca

    = 0.12 mol Ca



    • 1 mole of Na is the number of atoms in 22.9898g

      • 22.9898g is the molar mass

  • 1 mole H2O is the number of molecules in 18.015 g H2O

  • 1 mole H2 is the number of molecules in 2.016 g H2.


  • How many atoms are in 1 mol of H?

  • What is the mass of 1 mol of H?

  • How many atoms are in 2 mole of H?

  • What is the mass of 2 mol of H?

  • 46



    More Practice:

    • Convert 589 g of Au to moles.

    • Convert 344 grams of Fe to moles.

    • What is the mass of 3 moles of KOH?

    Mole Day is October 23rd!

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