Unit: Chemistry

Lesson 1: Introduction to Atoms

Essential Questions:1.) How did atomic theory develop?2.) What is the modern model of the atom?

How did atomic theory develop?

Atomos “uncuttable”

The smallest particle Atom

of an element

Dalton

Atoms cannot be broken into smaller pieces

Dalton thought that atoms were like hard balls that could not be broken.

Dalton’s Model.

Thomson Atoms are made of smaller parts

Negatively charged particles Electron

in an atom

Atoms contain a positive charge

An atom has electrons scattered throughout it like seeds in a watermelon.

Thomson’s ModelThomson suggested that atoms had negatively charged electrons set in a positive sphere. Each electron is represented by the symbol e−.

Rutherford

An atom is mostly empty space with a positive center

The center of an atom Nucleus

Positively charged particles Protons

in an atom’s nucleus

The pit models the nucleus of an atom and the fruit is the space with electrons.

Rutherford’s ModelAccording to Rutherford’s model, an atom was mostly open space. The “6+” in the model means that there are six protons in the nucleus.

Bohr

Electrons are found in specific orbits

Cloud Model

Electrons move within a cloudlike region

The amount of energy Energy level

an electron has

Modern Model of the Atom

Particles in the nucleus Neutron

with no electrical charge

An atom has a nucleus made of positively charged protons and neutral neutrons. The nucleus is surrounded by a cloud of negatively charged electrons.

Modern Model of an AtomA carbon atom has a nucleus made up of positively charged protons and neutral neutrons. The nucleus is surrounded by a cloud of negatively charged electrons.

Particle Charges

Number of protons = number of electrons

Particle Masses

Protons and neutrons make up most of the mass

The number of protons Atomic Number

in the nucleus

Atoms with the same Isotopes

number of protons and

different numbers of

neutrons

The sum of the protons Mass number

and neutrons in the atom

Isotopes of CarbonAll isotopes of carbon contain 6 protons. They differ in the number of neutrons. What is the missing information for each isotope?