Valence Electrons and Chemical Bonds, Exams of Chemistry

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Valence Electrons

Everything that is underlined should get filled in on your notes!

Valence Electrons

• Valence electrons
  • the electrons that are in the highest (outermost) energy level
  • that level is also called the valence shell of the atom
  • they are held most loosely

• Atoms usually react in a way that

makes each atom more stable.

• There are two ways this can

happen:

• The number of valence electrons

increases to eight

• Loosely held valence electrons

are given up

Chemical Bonds

• A chemical bond is the force of attraction that holds two atoms together as a result of the rearrangement of electrons between them.
• There are two types of chemical bonds: - Ionic - Covalent

Patterns on the Periodic Table

— The number of valence electrons increases as you go across the periodic table. — When you start each new period, the number of valence electrons drops down to one and begins increasing.

Drawing Atoms

• When scientists draw atoms to show how they chemically bond, they only draw the valence electrons.
• We only use the valence electrons because those are the only ones involved in chemical bonding.

— All atoms want a full valence shell (because that is how they become stable!) — So, they will share or transfer electrons with other atoms to achieve stability. — Nega;ve ions form when atoms gain electrons. — Posi;ve ions form when atoms lose electrons.

Steps for drawing an Electron Dot Diagram

1. Write the element’s chemical symbol
2. Look on the periodic table to see what group the element is in
3. Use the chart in your notes to determine how many valence electrons the element has
4. Draw the dots around the chemical symbol starting at the top and moving clockwise around the symbol

Try these on your own:

Electron

Configuration:

Ions and Excite State

Electron Configuration - Anions

• Anions – gain electrons – non-metals
• Electron Configuration:
  • Chlorine – 17 electrons in its neutral state
    • 1s 2 2s 2 2p 6 3s 2 3p 5
  • Chlorine ion
    • Gains 1 electron
    • New configuration: 1s 2 2s 2 2p 6 3s 2 3p 6
    • Notice that the electron configuration is the same as the noble gas Argon
    • This indicates that by gaining 1 electron, it obtains an outer octet (stable valence configuration!)

Electron Configuration

• Both ions obtain a noble gas configuration
• This makes the ion and the noble gas isoelectronic
• Isoelectronic: when two elements and/or ions have the same electronic configurations with one another
• They tend to have similar chemical properties.

Ionic configuration problems

Cations

• Determine the electron configuration for:
• Aluminum - Al
• Calcium – Ca
• Potassium - K
  • Anions
• Determine the electron configuration for:
• Nitrogen – N
• Fluorine – F
• Oxygen - O