Chem131 - General Chemistry I

Key terms and concepts needed to pass

John Dalton’s Theory of the Atom

1) Atoms are indestructible particles that make elements (REFUTED)

2) atoms of one element cannot change to other atoms of another element (REFUTED)

3) all atoms of an element have the same mass and properties (REFUTED)

4) atoms can bind in integers to form compounds

Refutes

1) Atoms can be broken down into protons, electrons, and neutrons

2) atoms can be isotopes, asotopes, or Ions, which don’t have the same mass

3) atoms can change into other atoms through radioactivity

Subatomic particles

Protons —> 1.67262 × 10^-27 —> +1 charge

Neutrons —> 1.67493 × 10^-27 —> 0 charge

Electrons —> 0.00091 × 10^-27 —> -1 charge

Protons

abbreviation = p+

~ identity of element

~ found by atomic # (z)

~ if two atoms have same # of protons, it is the same element

Neutrons

abbreviation = n0

~ keep atoms stable

~ too many protons or neutrons, an atom can shed a proton, changing its identity

~ acts as a buffer between protons in the nucleus

Electrons

abbreviation = e-

~ drives reactivity

~ Same # of electrons = same # of protons

~ if perfect amount of electrons = no bonds created

~ if perfect number is not achieved = react by gaining or losing electrons

• whichever requires less energy

• lose electron = positive charge = cations

• gain electron = negative charge = anions

Isotopes

two atoms with same number of protons but different number of neutrons

ex. C-12 & C-14 (carbon and carbon dating), CO-60 & CO-59 (radiation therapy)

Atomic models throughout the years

• Dalton’s Theory of Atoms

• Plum Pudding - an atom contains small negatively charged particles called electrons, and electrons exist in a positively charged space

• Nuclear model of the atom - 1) Most of the atom’s mass and all of its positive charge are contained in a small core (nucleus). 2) The volume of the atom is empty, throughout which tiny negatively charged electrons are dispersed. 3) Many negatively charged electrons outside the nucleus are positively charged protons in the nucleus —> keep the atom electrically neutral

• Bohr model - nucleus remains the same, electrons are in concentric orbits at a fixed distance from the nucleus

  1. energy is represented as concentric rings; specific levels —> discrete

  2. electron releases energy when transitioning from a higher to a lower energy

     1. seen as photons (light energy)

• Quantum Model - nucleus remains same, electrons don’t orbit but exist in probability dense domain that predicts positions

  • exist in all areas at the same time, we must measure its positions exist in order to see it in that moment

  • Electrons exist as waves until measured, then they become particles

Quantum numbers

• n = principle quantum number (energy level)

• l = angular momentum quantum number (orbital type)

• Ml = magnetic quantum number (which orbital) —> s,p,d,f

• Ms = magnetic spin quantum number

Pauli Exclusion Principle

no two electrons can have the same 4 QNs

Coulomb’s law

charge and repulsion

• particle of like charges repel (energy lowers when they separate)

  • allowing like charges to occupy space at a distance

• particles of unlike charges attract (energy lowers when closer together)

  • gets funny because all the atoms want to be near nucleus

• larger the charges, larger the energetic effect

  • bigger charge = stronger energy attraction = lower energy position

Shielding and Effective Nuclear charge

total amount of attraction an electron feels for nucleus’s protons

the electrons want be as close to the nucleus as possible

Penetration

the shape of orbitals allow electrons the possibility to get closer to the nucleus, which lowers its energy overall

Aufbau Principle

electrons enter atomic orbitals from lowest energy to highest

Hund’s rule

electrons will always enter empty orbital before they pair up