Atoms

What did Democritus propose about atoms around 400 BC?

All matter is composed of atoms.

What was Aristotle's view of matter in 400 BC?

Matter is made out of 5 elements.

What model did John Dalton create in 1803?

Solid sphere model.

What significant discovery did J.J. Thomson make in 1903?

Electrons exist.

What aspect of the atom did Ernest Rutherford discover in 1911?

The nucleus is positively charged.

What did Niels Bohr propose in 1913 about electrons?

Electrons orbit the nucleus and are negatively charged.

What does the quantum model proposed by Schrödinger and Heisenberg in 1926 state?

Electrons can’t be pinpointed.

What is Atomic Theory?

All matter is made of atoms, which are the smallest units of matter.

What are the three subatomic particles?

Protons, neutrons, and electrons.

What charge do neutrons have?

No charge.

What charge do electrons carry?

A negative charge.

What charge do protons have?

A positive charge.

What does the atomic number represent?

The number of protons in the nucleus.

How is atomic mass calculated?

The number of protons plus the number of neutrons.

What is an isotope?

A variation of the same type of atom.

What are valence electrons?

Electrons in the outermost shell.

What defines an element?

A bunch of the same kinds of atoms together.

Who organized the elements by atomic mass in 1869?

Dmitri Mendeleev.

What information does the atomic number provide?

The number of protons in an element.

What does Fe stand for in chemistry?

Iron.

What is the average atomic mass of Iron?

55.8.

How many natural elements are there?

1-92.

What elements are numbered 93-118?

Man-made elements.

What are metals characterized by?

Good conductors, malleable, ductile, and variety.

What are non-metals characterized by?

Poor conductors, brittle, and mostly gases at room temperature.

What is a metalloid?

A semi-metal that can conduct under certain conditions.