CEM 141 MSU Exam 3

Ionization Energy

energy required to remove an electron from an atom in the gas phase

Left Side Electrons

have weaker attractions to remove electrons

easier to remove electrons from the left side of the table than the right side

Does it take MORE or LESS energy to remove an electron from Li than from Na?

MORE

Why? Because as we move down a group, the orbitals become larger and weaker. While going across the effective nuclear charge increases. (holds onto the electrons tighter)

Big Bang evidence

universe is expanding (red shift)

Where do atoms come from?

The Big Bang

What were elements formed by?

Nuclear reactions

Chemical reactions

involve rearrangements of valence electrons

the element undergoing a chemical reaction does not ever change

Ionization energies are affected by

-size of an atom

-size of positive charge

Periodic Trends

-small atoms have higher ionization energies

-they are inversely related

Atomic Radius Decreases ----> Ionization energy increases

when the radius decreases, it pulls the electrons closer. decreasing the size of an atom

Nuclear Reactions

Fusion and Fission

Fusion

two lighter nuclei combines to form a heavier nucleus (energy released)

Fission

a heavier nucleus is broken a part to form lighter, more stable nuclei energy

Atomic # =

# of protons

Atomic mass =

what's left over

Do isolated atoms or molecules have melting or boiling points?

No

Do isolated atoms or molecules exist in a state (solid, liquid, gas)?

No

Why do bonds form between atoms?

because valence electrons are attracted to the nuclei of other atoms

Covalent Bonds

two hydrogen atoms interact and form a covalent bond

What properties do metals have?

-hard

-conduct electricity

-shiny

-react w/water

-malleable

Bonding in Metals

atomic orbitals combine with each other to form molecular orbitals

Covalent bonds hold atoms together within..

molecules

Molecular interactions hold atoms together between...

molecules

T/F: Covalent bonds are stronger

True

Why are metals shiny?

photons of wavelengths are absorbed and then re-emitted

Changes of state (solid --> liquid ---> gas)

REQUIRES energy

Changes of state (gas --> liquid --> solid)

RELEASES energy

Where does the energy come from?

The surroundings

Where are the attractions coming from?

Between the molecules

Ionic Bonds -

are between a metal and non-metal

Bonding in Diamond

each carbon atom is bonded to make more carbon atoms

Valence Bond

atomic orbitals overlap to form a bond

Bonding in Graphite

one s and two p orbitals hybridize to give three Sp2 orbitals

Heterogeneous Compounds

bonding in carbon compound bonds to C,H,O,N,S,P

Lewis Structure

1. group number = how many valence electrons

2. for cations = (+) remove electrons

3. for anions = (-) add electrons

4. use 2 electrons for each atom

Formal Charge:

Valence electrons on free atom - #bonds to atoms - non bonded electrons = Formal charge

Example: OH-

6 from oxygen +1 from hydrogen +1because its minus 1 ion = 8 valence electrons

Electronegativity

ability of an element to attract electrons to another electron

Electronegativity ...

increases across the table

decreases down the table

Polar Bonds

when two atoms of different eleectronegativities bond, the electrons are not shared equally

- results in dipole

Which Bonds are Polar?

H-F

H-O

CH3F

H20

Which Bonds are Not Polar and have similar electrongeativity

H-C

C-C

CF4

CO2

SO3

Triple Bonds

C - sp hybridized

One sigma bond

Two pi bonds

Types of Intermolecular Forces

LDFS

Dipole-dipole interactions

Hydrogen bonds

London Dispersion Forces

-Present in all substances

-Temporary fluctuating dipoles

-Depends on size, surface area, and shape of molecule

Lewis Dot Structure for H2O

Dipole-dipole Interactions

-Present in polar substances (along with LDF)

-Typically stronger than LDF

Examples: HCL, CH3, CH2O,Ch3OCH3

Hydrogen Bonding Interactions

-Present between two molecules

-H-bonds are extremely strong dipole interactions

Examples: H2O, CH3OH, CH3Ch2OH, HF, NH3