Unit 2 Atoms and States of Matter

proton

+ charged particle in the nucleus of an atom

electron cloud

- charged region surrounding an atom's nucleus where one or more electrons are most likely to be found

isotope

Atoms of the same element that have different numbers of neutrons

atom

Basic unit of matter Smallest particle of an element

Atomic theory development

Democritus -coined term "atoms" meaning indivisible; all matter is composed of atoms John Dalton -all matter is composed of atoms -atoms of the same element are identical; atoms of different elements are not identical -different atoms make compounds JJ Thomson -Plum pudding model (also known as chocolate chip cookie model) -Atoms contain negative electrons Ernest Rutherford - atoms are mostly empty space - core of positive particles Niels Bohr -Planetary model: Electrons are arranged like planets around the sun in shells around the nucleus which contains positive protons Schrödinger and Heisenburg Quantum mechanical model or Cloud model. Atom has cloud-like region where electrons move in levels with other electrons with the same energy. Unlike the Bohr model, the quantum mechanical model does not define the exact path of an electron, but rather, predicts the odds of the location of the electron. This model can be portrayed as a nucleus surrounded by an electron cloud. Where the cloud is most dense, the probability of finding the electron is greatest, and conversely, the electron is less likely to be in a less dense area of the cloud. Chadwick -The nucleus contains neutral charged particles called neutrons

nucleus

Dense + charged center of an atom Contains protons and neutrons

atomic mass

The average mass of all the isotopes of an element

electron

a - charged subatomic particle found in electron cloud

neutron

a subatomic particle that has no charge in the nucleus of an atom

ion

ion: A charged atom; An atom or group of atoms that has a positive or negative charge due to a gain or loss of electrons.

Atomic mass - Atomic number =

number of neutrons

neutral atom

same number of protons and electrons

electromagnetic force

the attraction or repulsion between charged particles. electromagnetic force holds negatively charged electrons to the positively charged nuclei of atoms.

atomic number

the number of protons in the nucleus of an atom

strong nuclear force

the powerful attractive force that binds protons and neutrons together in the nucleus

molecule

two or more atoms bonded together can be same element or different elements