Chemistry 1-4: Electrons in Atoms

Electrons in Atoms

Multiple Choice

Most of the mass in an atom is made up of _____________________?

• protons and electrons
• protons and neutrons
• neutrons and electrons
• electrons and quarks

Multiple Choice

What is the atomic number?

• the number of protons in the nucleus

• the number of protons and neutrons in the nucleus

• the number of neutrons in the nucleus

• the number of protons in the energy levels

Multiple Choice

What is the mass number?

• the number of protons in the nucleus

• the number of protons and neutrons in the nucleus

• the number of neutrons in the nucleus

• the number of protons and electrons in the atom

Multiple Choice

What is the atomic number of this atom?

• 1

• 3

• 4

• 7

Multiple Choice

In order for an atom to be neutral what has to be true?

• The atom has more protons than neutrons
• The atom has more neutrons than protons
• The atom has the same number of protons and neutrons
• The atom has the same number of protons and electrons

Lesson Objectives

• Identify the different blocks of the periodic table

• Describe the electron configurations using different methods

• Draw Valance electron structures for different atoms

Organizing the Periodic Table

• The periodic table is organized into periods and groups

  • Periods: Horizontal Rows

  • Groups: Vertical Columns

• We can divide the periodic table into different blocks based on the highest-level subshells with electrons

  • s

  • p

  • d

  • f​

S-block

P-block

d-block

f-block

Electron Configurations​

• Electron Configurations: The way in which electrons are arranged in various orbitals around the nuclei of atoms

  • Electrons fill orbitals following certain rules​

  • Energy plays a major role in how electrons arrange themselves in an atom

  • Three rules for Electron Configurations

The Aufbau Principle

• The Aufbau Principle: Electrons occupy the lowest energy sub-shells first​

  • This makes elements more stable

  • the 1s orbitals will always fill before the 2s orbitals

  • Order: 1s, 2s, 2p, 3s, 3p, 4s, 3d, 4p....

    • d sub-shells always a lower energy level than the rest of the period

  ​

Hunds Rule

• Hunds Rule: In sub-shells with multiple orbitals (p, d, f), all orbitals must be filled before getting a second electron

  • Every orbital has to get an electron before getting seconds

Pauli's Exclusion Principle

• Pauli's Exclusion principle: electrons in the same orbital can not be in the same spot at the same time

  • Spin: a property of electrons that describes their orientation in an orbital

  • We show this with two verticle arrows pointing in opposite directions

Writing Electron Configurations Sample Problem 1

• Step 1: Use the Atomic number to determine the number of electrons

  • Example: Oxygen​

Writing Electron Configurations Sample Problem 1

• Step 1: Use the Atomic number to determine the number of electrons

  • Example: Oxygen​ has the atomic number of 8, so it has 8 electrons

• Step 2: Use arrows to represent the number of electrons in each orbitals

  • Start in the 1s sub-shell

  • Each orbital in a shell has to get an electron before it can get a second one

  • Electrons in the same orbital spin in opposite directions​

Writing Electron Configurations Sample Problem 1

• Step 1: Use the Atomic number to determine the number of electrons

  • Example: Oxygen​ has the atomic number of 8, so it has 8 electrons

• Step 2: Use arrows to represent the number of electrons in each orbitals

  • Start in the 1s sub-shell

  • Each orbital in a shell has to get an electron before it can get a second one

  • Electrons in the same orbital spin in opposite directions​

Writing Electron Configurations Sample Problem 2

• Write the Electron Configuration for Nickel

• Step 1: Use the Atomic number to determine the number of electrons

Writing Electron Configurations Sample Problem 2

• Write the Electron Configuration for Nickel

  • Step 1: Use the Atomic number to determine the number of electrons

    • Example: Nickel has the atomic number of 28, so it has 28 electrons

  • Step 2: Use arrows to represent the number of electrons in each orbitals

    • Start in the 1s sub-shell

    • Each orbital in a shell has to get an electron before it can get a second one

    • Electrons in the same orbital spin in opposite directions​

Writing Electron Configurations Sample Problem 3

• Write the Electron Configuration for Silicon

• Step 1: Use the Atomic number to determine the number of electrons

Writing Electron Configurations

• Step 1: Use the Atomic number to determine the number of electrons

  • Example: Silicon​ has the atomic number of 14, so it has 14 electrons

• Step 2: Use arrows to represent the number of electrons in each orbitals

  • Start in the 1s sub-shell

  • Each orbital in a shell has to get an electron before it can get a second one

  • Electrons in the same orbital spin in opposite directions​

Writing Electron Configurations

• Step 1: Use the Atomic number to determine the number of electrons

  • Example: Silicon​ has the atomic number of 14, so it has 14 electrons

• Step 2: Use arrows to represent the number of electrons in each orbitals

  • Start in the 1s sub-shell

  • Each orbital in a shell has to get an electron before it can get a second one

  • Electrons in the same orbital spin in opposite directions​

Exceptions to Electron Configuration Rules

• Some elements do not follow the normal electron configuration rules that others do

  • Chromium: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d⁵ 4s¹

  • Copper: 1s² 2s² 2p⁶ 3s² 3p⁶ 4s² 3d¹⁰ 4s¹

Noble Gas Configurations

• Electron Configurations can get long

• Noble Gases: the last group of the periodic table

• You can shorten the writing by starting with the Noble Gas before the element, and only writing what is in the period of the component in questions​

Noble Gas Configuration Sample Problem 1

• Write the Noble Gas Configuration for Sulfur​

  • Step 1: Identify the Noble gas that comes before sulfur

    ​

Multiple Choice

Which Nobel Gas come before sulfur?

• Helium

• Neon

• Argon

• Krypton

• Xenon

Noble Gas Configuration Sample Problem 1

• Write the Noble Gas Configuration for Sulfur​

  • Step 1: Identify the Noble gas that comes before sulfur

    • The Noble Gas before sulfur is Neon

  • Step 2: Write Neon's Chemical Symbol in Brackets

  • Step 3: Continue the configuration from where Neon is

    • Shortened Configuration: [Ne] 3s¹3p⁴

    ​

Noble Gas Configuration Sample Problem 2

• Write the Noble Gas Configuration for Potassium

  • Step 1: Identify the Noble Gas that comes before Potassium.​

Multiple Choice

Which Nobel Gas come before Potassium?

• Helium

• Neon

• Argon

• Krypton

• Xenon

Noble Gas Configurations Sample 2

• Write the Noble Gas Configuration for the element Potassium

  • Step 1: Identify the Noble Gas that comes before Potassium

    • The noble Gas before Sulfur is Argon (Ar)

  • Step 2: Write Argon's Chemical Symbol in Brackets

  • Step 3: Continue the configuration from where Argon is

    • Shortened Configuration: [Ar] 4s¹​

Valence Electrons

• Electrons in an element are divided into two groups

  • Core electrons:​ exist in the inner and lower energy shells

  • Valence Electrons: electrons in the outermost p energy shell

    • are most involved in reactions

    • are unstable unless they have a full electron shell

      • Noble Gases have a full shell, which is why they don't react

      • The Octet Rule: Atoms are most stable when they have a total of eight electrons in their outer shell, and will respond to gain or lose the electrons needed

Identifying Valence Electrons

• ​Counted by Looking at the Group numbers

  • Group 1=1, Group2=2

  • Groups 13-18: Valence electrons = Group number-10

    • Group 13=3, Group 14=4, Group 15=5, Group 16=6 Group 17=7, Group 18=8

• Shown Using Electron Dot Structures​

  • A visual representation of the valence electrons in an element​

Valence Electrons Sample Problem 1

• ​Sample Problem: Draw the electron dot structure for Sodium

  • Step 1: Identify which group Sodium is in

Multiple Choice

Which Group is Sodium in?

• 1

• 2

• 12

• 14

• 16

Valence Electrons Sample Problem 1

• ​Sample Problem: Draw the electron dot structure for Sodium

  • Step 1: Identify which group Sodium is in

    • Sodium is in group 1 so it has 1 Valance Electron

  • Step 2: Write the Element symbol

  • Step 3: Draw dots around the Symbol, one for each valance electron

    • Start at the top and go clockwise

    • Don't Double up until all four sides have one​

Valence Electrons Sample Problem 2

• ​Sample Problem: Draw the electron dot structure for the Silicon

  • Step 1: Identify which group Silicon is in

Multiple Choice

Which Group is Silicon in?

• 1

• 2

• 13

• 14

• 16

Valence Electrons Sample Problem 2

• ​Sample Problem: Draw the electron dot structure for the Silicon

  • Step 1: Identify which group Sodium is in

    • Silicon is in group 14 and has 4 Valance Electrons

  • Step 2: Write the Element symbol

  • Step 3: Draw dots around the Symbol, one for each valance electron

    • Start at the top and go clockwise

    • Don't Double up until all four sides have one​

Valence Electrons Sample Problem 3

• ​Sample Problem: Draw the electron dot structure for Chlorine

  • Step 1: Identify which group Chlorine is in​

Multiple Choice

Which Group is Chlorine in?

• 2

• 13

• 13

• 14

• 17

Valence Electrons Sample Problem 3

• ​Sample Problem: Draw the electron dot structure for Chlorine

  • Step 1: Identify which group Chlorine is in

    • Chlorine is in group 17 and has 7 Valance Electrons

  • Step 2: Write the Element symbol

  • Step 3: Draw dots around the Symbol, one for each valance electron

    • Start at the top and go clockwise

    • Don't Double up until all four sides have one​

Draw

Draw the electron dot structure for sulfur

Draw

Draw the electron dot structure for calcium

Hotspot

Click all the Valence electrons in this atom.

Multiple Choice

How many valence electrons are in this element?

• 7

• 6

• 5

• 2