Unit 2 - Modern Atomic Theory

"Seeing" Atoms

smaller than a wave of visible light & cannot be seen with light microscope.

Democritus (460-371 BC)

• was the first to say that all matter is composed of atoms

Robert Boyle (1627 - 1691)

defined element as sample of matter which cannot be broken down

John Dalton’s Atomic Theory

atoms of different elements combine to form compounds

J.J Thompson

discovered the electron using cathode ray tube

pierre joseph pelletier (1817)

discovered chlorophyll, caffeine, strychnine, colchicine, and quinine.

William Perkin (1856)

produced first synthetic dye he called mauve

William Thomson

Made plum pudding model

hantaro nagaoka (1904)

developed "saturnian" system with electrons orbiting around a nucleus in rings

earnest rutherford 

discovered that atoms have a dense nucleus and mostly empty spaced through gold foil experiment

niels bohr (1885 - 1962)

developed atomic model with distinct energy levels

wave mechanical model

- an electron is a particle and also a wave in an energy level

nuclear fission

- atom split

- atomic bomb

- nuclear power

silicon chip

- computer chip manufacture on large scale

nanotechnology

• working w batter as small as a nanometer

• synthetic molecules designed to function as molecule sized machines

how many orbitals do "s" sublevels contain?

1

how many orbitals do "p" sublevels contain?

3

how many orbitals do "d" sublevels contain?

5

how many orbitals do "f" sublevels contain?

7

orbital

• probability map of an electron

• each orbital contans up to 2 electrons

hund's rule

- each orbital of a sublevel must have 1 electron before an orbital of the same sublevel can have two electrons.

ex. Oxygen is 1s²2s²2p (each sublevel before the last has been filled to the brim)

excited electrons

• cannot remain excited

• will drop back down to a lower energy level

• gives off a photon of light as it drops in energy

photon

• tiny, massless particle that carries light and other electromagnetic energy.

• energy of the photon = energy lost by the electron

• energy of the photon determines the wavelength (color)

how does an electron reach an excited state?

when electrons absorb energy from heat, electricity, or light, they move to higher energy levels

Dmitri Mendeleev

• a russian chemist, listed the elements in vertical columns in order of increasing atomic mass.

Henry Moseley

arranged the elements on a periodic table in order of increasing ATOMIC NUMBER

periodic table law 

"when elements are arranged in order of increasing atomic number, there is a periodic pattern in their physical and chemical properties."

Horizontal rows in the periodic table are called..

Periods

Verticle rows on the periodic table are called..

groups or families

elements are divided into two main types called..

metals and nonmetals, with semimetals (metalloids) being in between.

main groups on the periodic table are called..

Noble Gases, Halogens, Alkali Metals, Alkaline Earth Metals, Transition Metals, Rare-earth elements

What are the Periodic Trends and why do they occur?

• atomic radius, ionization energy, and electronegativity.

• they occur due to the amount of attraction between the nucleus and valence electrons.

What makes a nucleus in an element more positive?

When the element has a larger number of protons, it increases the attraction to the valence electrons, so the electrons are pulled closer to the nucleus

How does each energy level "shield" the next?

As we move down a group, each element has one more energy level than the one before. By separating the energy level from the nucleus, it reduces the attraction of the valence electrons.

What is atomic radius?

• Distance from the nucleus of an atom to its valence electrons.

• greater atomic radius = greater size of the atom.

When does Atomic Radius Decrease vs INCREASE?

• Atomic radius DECREASES across a period from left to right because increased nuclear charge pulls electrons closer

• atomic radius INCREASES down a group due to the addition of new electron shells, which places valence electrons further from the nucleus. 

Ionization energy

• energy required to remove an electron from an atom.

• The FIRST ionization energy is to REMOVE the FIRST ELECTRON..  second ionization energy is to remove the second electron.. etc.

When does ionization energy increase vs decrease?

• it INCREASES across a period as a stronger nuclear charge holds electrons more tightly,

• It DECREASES down a group because increased electron shielding WEAKENS the nucleus's pull on valence electrons

Electronegativity

How strongly the nucleus of an atom attracts the electrons of another atom in a bond.

How does Electronegativity INCREASE vs DECREASE

• it INCREASES because more protons in the nucleus means greater attraction to the valence electrons of another atom.

• it DECREASES because increased shielding reduces the ATTRACTION of the valence electrons of another atom

define orbital

the probability map of the location of two electrons

define valence energy level

the highest principal energy level of an atom

structure of an atom

neutral neutrons and positive protons make up the nucleus, with negative electrons in distinct orbitals surrounding the nucleus

Explain the three trends moving left to right on Periodic Table.

Atomic radius decreases, ionization energy increases, and electronegativity increases. this is because the number of protons is increasing, which makes the nucleus more positive and more attractive to the valence electrons.

Explain the three trends moving up and down on the Periodic Table

Atomic radius increases, ionization energy decreases, and electronegativity decreases. The reason is that the number of energy levels is increasing which increases the shielding effect between the nucleus and valence electrons.