Chem 20AP Unit 1

The Diversity of Matter and Chemical Bonding

Law of Conservation of Matter

Matter cannot be created nor destroyed by chemical reactions

John Dalton’s Theory of the Atom

• Matter is made up of particles called atoms

• All atoms are identical

• Chemical reactions are just rearrangements of atoms

• Atoms are unchangeable

Thomson Atomic Model

• Determine the presence of the electron

• A cloud of positive charge with electrons embedded them

What is the Model Thomson created called?

Plum Pudding Model

How did the Rutherford Gold experiment work?

Beamed alpha particles at a gold leaf with a screen surrounding it that detects the alpha particles

What was discovered in the Rutherford Gold experiment?

• Fact that some particles passed thorugh the gold foil concludes that atoms are moslty empty space

• Fact that some particles bounced right back shows that there is a very dense core

• Fact that some were bent says that the centre of the atom is positive

Subatomic Particles

• Protons (+)

• Neutrons (0)

• Electrons (-)

Valence Electrons

Electrons in the outermost energy level

Cation

Positively charged ion when an atom loses an electron

Anion

Negatively charged ion when an atom gains an electron

What is an Ionic compound?

Compounds formed from the transfer of electrons

How do ionic compounds attract?

The formation of a cation and an anion which forms an ionic bond causing it to be electrostatically attracted

What is Electrostatic attraction? 

Attraction of its own electrons and oppositely charged particles

What is a formula unit

One ionic bond ratio

What is the name “hydrate” mean when writing its formula?

H2O

Orbitals

Specific volume of space where an electron is likely to be found

Electronegativity

Ability of an atom to attract bonding electrons within a bond

Electronegativity as you go up the group

Electronegativity increases because you have fewer electron shells. Less electron shielding.

Electron Shielding

describes how inner-shell electrons reduce the electrostatic attraction between valence electrons

Electronegativity as you go across a period

Electronegativity increases because you have more protons in the nucleus therefore a greater attraction of electrons

Why do metals have lower electronegativities?

Because they want to get rid of an electron, not gain one.

Why do nonmetals have higher electronegativities?

Because they want to gain an electron, not lose one.

Electronegativity difference of Ionic compounds

Greater than 1.7

What happens after the electronegativity difference surpasses 1.7?

This is the point when there is a complete transfer of electrons from the atom with the lower electronegativity to the higher electronegativity.

Shape of ionic compounds

Forms a crystal lattice shape to maximize total attraction between cations and anions

Ionic bonds, bond direction

They are non-directional because the ion has same attraction in all directions. This makes it very strong.

Ionic Property: Hard

Crystal lattice and their bond direction is really hard to break

Ionic Property: Brittle

Crystal lattice cannot be rearranged without breaking it

Ionic Property: High melting/boiling point

Ionic bonds require lots of energy to break because of its bond direction

Ionic Property: Most are soluble in water

Attraction between the polar property of water and the ions

Ionic Property: Conductive

Conductive due to the ions being “spread out” and moving so it can create a current

Ionic Property: stable at SATP

Valence shells are full

Molecule

Independent unit made up of nonmetallic atoms held by covalent bonds

Covalent bonds

Unstable atoms with incomplete valence shells share electrons to increase stability

How do covalent bonds work?

Shared pair of electrons that creates a strong directional intramolecular force

Chemical bond

Balance of attracted and repulsive forces

Bond energy

Energy required to break a bond

Bond length

The distance between two nucleus in a bond.

Why are multiple bonds stronger than single bonds

Because they have a higher force of attraction = shorter bond length

Diatomic elements

Two atoms of the same element joined by a covalent bond

Intramolecular Force

Forces within a molecule (Between atoms)

Electronegativity of molecular compounds

1.7 or less

Bonding capacity

Maximum number of sinlge covalent bonds that an atom can form

VSEPR Theory

The shape a compound makes and states that atoms try to stay as far as possible because the electrons repel each other

Nonpolar Covalent bond

Symmetrical electron charge distribution

Polar covalent bond

Electrons spend more time closer to one atomic nucleus than the other

Electronegativity difference in nonpolar covalent bonds

0.4 or less

Electronegativity difference in polar covalent bonds

Greater than 0.4 but less than or equal to 1.7. The greater the difference, the more polar it is.

Factors that make a molecule nonpolar

• No polar bonds

• Terminal atoms are all the same

Factors that make a molecule polar

• At least one bond is polar

• One terminal atom is different

What is used to show bond polarity?

Bond dipole

Intermolecular forces

Forces of attraction and repulsion between molecules

Strength of intermolecular forces

Weaker than covalent bonds (intramolecular forces)

Dipole-Dipole force

Attraction between permanent dipoles

Dipole-Dipole force strength

The more polar the molcule, the stronger the dipole-dipole force

London (dispersion) Force

Momentary attraction because of temporary dipoles

London (dispersion) Force strength

The more electrons there are, the stronger the force of attraction. (count the total number of electrons)

Isoelectronic molecules

Have the same number of electrons so they have the same london force

Hydrogen Bonding

Hydrogen atom is bonded to a strongly electronegative atom with a lone pair of electrons

Why are hydrogen bonds so strong?

Highly electronegative atom pulls the hydrogens electron so strongly it becomes attracted to the hydrogen proton.

What can hydrogen make hydrogen bonds with?

N, O, F

Enthalpy of fusion

Amount of energy required to change one mole of substance from a solid to liquid. (More condense —> Less condense)

Enthalpy of Vaporization

Amount of energy required to change one mole of substance from liquid to gas

Predicting relative boiling points

• Only LDF present but one substance has greater LDF

• Same LDF but one has dipole-dipole or hydrogen bonds, or both

• One substance has greater LDF and has dipole-dipole or hydrogen bonds, or both