Chemistry Unit 5

Electrons

the negatively charged particles in an atom that add no mass and exits in the electron cloud

Nucleus

A dense positively charged center in an atom containing protons

Protons

Positively charged particles in the nucleus of an tom (the number of protons determines what an atom is)

neutron

electrically neutral particle that has the same mass as a proton and is found in an atoms nucleus. Play a role in an atoms radioactivity

Atomic number

Number of protons in the nucleus of each atom of a given element; is the top number on the periodic table

Isotopes

two or more atoms of the same element that have different numbers of neutrons in their nuclei.

Ion

an atom or molecule with a net electric charge due to the loss or gain of one or more electrons.

Mass number

sum of the number of protons and neutrons in the nucleus of an atom

Stable

If an isotope is radioactive, or spontaneously breaks up, this means that the isotope has an unstable number of neutrons, and will decay.

Radioactive

an element whoose atoms have an unstable amount of nuclei. Over time the nuclei decay into a different type of atom with a more stable nucleus.

Democritus

430BCE, he proposed that all matter was formed of small particles that couldn’t be cut into even smaller particles (word for these was atomos)

Atom

the smallest particle that can still be considered an element.

John Dalton

early 1800’s got the ball rolling again with a focus on what atoms and elements really are.

J.J. Thompson

late 1800’s discovered that atoms contain negatively charged particles which we now call electrons. He also inferred that atoms must have positively charged particles. Came up with chocolate chip cookie method.

Chocolate-chip-cookie model

negatively charged electrons are randomly scattered in a sea of positive particles, like chocolate chips in a cookie.

Ernest Rutherford

early 1900’s found that atoms contain mostly empty space except for a dense positively charged center the nucleus, containing positively charged particles called protons using the gold foil expirement

The gold foil expirement

Rutherford shot positively charged particles at gold foil, 1 in 20,000 bounced back rather than passed through the foil (foil acted as a net sometimes)

Niels Bohr

early 1900’s he suggested that electrons move in specific 2-d orbits around the nucleus, like moons orbiting the planets.

What do we know about electrons now

electrons don’t actually move in set orbits like planets, they move around in different energy levels in a cloud region called the electron cloud, outside of the nucleus. this cloud like region makes up most of the atoms volume

James Chadwick

early 1930’s found that not all of an atoms mass was accounted for by previous models. He found the neutrons, which he determined were located in the nucleus.

Dmitri Mendeleev

a Russian scientist who discovered a set of patterns that applied to all elements of the periodic table in the mid 1800’s, he knew that some of the elements had similar physical and chemical properties

How was the og PTE arranged

it was arranged average atomic mass

Average Atomic Mass

the average mass of a known isotope of an element (expressed as amu) Number on the bottom of the element

to find mass number

the average atomic mass rounded to the nearest whole number

Mass number

the mass of any one given atom of that element (protons + neutrons)

Periodic table

a chart that shows all of the elements arranged according to the repeating pattern of their properties

How is the modern PTE arranged

by increasing atomic number

Vertical columns

groups of families (elements within a family have similar properties)

Horizontal rows

called periods

Chemical symbol

1-2 letters, first letter is uppercase second letter is lowercase

if both letters are uppercase it is…

a compound

If it has a neutral charge, it..

has the same number of protons and electrons.