Atomic Theory and Periodictiy

Law of conservation of mass

Mass is neither created nor detroyed

Law of definite proportion

A given compound always contains exactly the same proportion of elements by mass

Daltons atomic theory

• Elements are made out of atoms

• Two of the same elements have identical atoms

• Chemical compounds are formed when atoms are combined with eachother

• Chemical reactions involve the reorganization of the atoms

Isotopes

• Elements that have different numbers of neutrons but the same amount of protoms.

• Reffered with their mass

• Some of them are stable, some of them are radioactix (unstable)

Atomic mass

Protons + number of neutrons (atomic number - mass number). Must be a whole number

Electromagnetic radiation (photon)

Radient energy that exhibits wavelike behaviour and travels speace at the speed of light

ie. Visible light, heat, X-rays, radio waves

Atomic spectra

• Light could be sperated into its components displayed as a spectrum

• The pattern of the spectra were distinct for each element.

Bohrs understanding

• Electrons only exist only at the discrete(energy levels). They don’t loose energy if they stay at thos elevels

• Electrons only absorb energy of certain wave length (Proven because atoms don’t emit a continous of rainbows

• Electrons could only possess certain amounts of energy

Quantum jumps

• The instaneous transition of an electron between descrete, fixed energy levels within an atom or molecule.

• They either absorb a photon (jump up an energy level) or emit a photon (Goes down an energy level)

Absorption Spectra

• Atoms/ molecules can absorb light or specfic energy (colour) to move an electron to a higher energy level by exciting them.

• Photons that are absorbed correspond to a specfic wave length of light, which correlates to a black line in a continuous spectrum.

• Energy levels must be discrete (exact)

Emmision spectrum

The unique pattern of specific wave lengths (colours) of light emmited by an atom or compound when its electrons transition from higher, excited energy level to a more stable energy levels. Releasing photons with energy equal to the energy difference

Electrons

• Mass of an electron is very small, but large compared to light

• Thus, it has characteristics of a particle but also wavelike behaviour. So, it can be assumed that electrons ar like standing wave lengths

Standing wave lengths characterists

• There are four nodes (two wave lengths that are made into a circle)

• They must be whole numbers

• Add the correct number of energy, the wave will exspand

Uncertainty principle

It’s impossible to know both the exact position and speed of a particle because we’d have to shine energy on it, thus changing its position and speed.

Orbitals

• Each contain two electrons

• Electron shells around an atom are made out of subshells, which are made out of orbitals.

• The space repersents a 90% chance of finding an electron

Electron probability density

• The likelihood of finding an electron in a specific region of space, which is visualized as orbitals.

• The denser areas means theres a higher chance of finding the electron.

s subshell

• Contaisn the 1s orbital

• Spherical in shape

• Lowest energy orbitals of the shell

• 2 electrons fit

p subshell

• Made up of 3p orbitals

• Dumbell shaped, or has two lobes on either side of the nucleus and oriented different

• Holds up to 6 electrons

• In the second shell, there is:

  • One 2s orbitals

  • Three 2p orbitals

d subshell

• Weird shapes

• 5d orbitals in the subshell

• Can hold up to 10 electrons

The relationship between the position of elements, their properties, and their electron configurations

• Arrnaged so that one period (row) is equal to one shell, and each group (column) is the number of valence electrons and the blocks are the type of subshells filled.

• This makes the periodic table a electron configuration map in essence.

Atomic radius

• The measure of an atom's size, defined as the distance from the center of the nucleus to the outermost electron shell.

• Decreases moving from left to right across a given period

  • Because you’re adding protons to the nucleus and more electrons into the same outer shell, which increases attraction.

• Increases moving to the bottom down a family

  • Because new electrons shells are added, which increases the distance from the nucleus

Ionic radius

• Positive ions have their electron removed, so they are smaller then their atoms.

  • Ie. Since we are removing a shell, the radius gets smaller. That’s why cations get smaller.

• Negative ions have electrons added to their shells, so they become larger.

  • The number of protons in the nucleus hasn’t changed nor has the number of electron shells. But since there are more electrons on the outer most shell, this causes repulsion.

• Increases down a group, decreases across a period

Ionization energy

• The minimum energy required to remove the outermost, most loosely bound electron from a neutral gaseous atom/ molecule.

• A small IE means its easy to overcome the attraction of the electron from the nucleus, thus ripping the electron off.

• Drops descending down a family

  • Valence electrons are further from the nucleus, therefore less attracted

  • The shells of inner electrons cause shielding, and reduce attraction between the nucleus and the outer electrons

Electron affinity

• The energy change asscoiated with the addition of an electron

• Large negative value: A lot of energy is realeased= Easy and spontaneous

• Large, positive value: A lot of energy is required= Hard, non- spontaneous

Electronegativity

• The ability of an atom in a molecule to attract shared electrons to itseld

Reactivity

• Assciated with IE and EA. Which are in turn associated with

  • # of protons

  • # of electron shells

Alkali metals

• More reactive as you progress down a family

• Size gets larger. Causing shielding because of the increase number of electron shell.

  • So the valence electrons are easy to remove + tranffered to hydro atoms

• Melting point decreases as you progress down the family

• Metalic character:

  • Decreases across a period, tendency to attract valence electrons increases

  • Increases lower in a family because valence electrons are more easily liberated

Halogens

• Reactivity Decreases as you progress down a family

• Increase size and shielding leads to familial decrease

• Melting point increase within a family

IE variation

• Ie increase as atmoic radius decreases

• IE increaseed when s subshell is full

• IE drops a bit when moving to a new subshell

• IE increase again when the subshell is half full

• Then decreases again and continues to increase towards noble gases

Successive ionization energies

• Removing successive electrons requires more energy beucause of the increased attraction between the electrons and the protons

• Removing electrons from the same shell has a gradual increase

• When electron from an inner shell is removed, the IE jumps

Oxide compounds trends

Oxide compound

• As metallic character decreases, electronegativity increases

• Oxygen either retains electron from metals and form ionic bonds, or shares them with non-metals in a covalent bond, or something inbetween

• Ionic bonds = basic, molecular= acidic