Atoms and Elements

The smallest part of an element that can be identified as that element is

• nucleus.
• atom.

The first person to suggest the existence of atoms was

• Dalton.
• Democritus. 

All atoms of the same element have the same

•  atomic mass. 
•  atomic number

A positively charged particle is

• electron.
• proton.
• neutron

The element with the smallest atomic number is

• nitrogen.
• hydrogen. 
• sodium
• helium

To calculate the atomic mass of an element, you must know the mass of its

• neutrons.
• protons and neutrons

The second energy level of an atom can hold

•  32 electrons. 
•  8 electrons

In the periodic table, elements are arranged in order of

• decreasing atomic number
•  increasing atomic number

Vertical columns on the periodic table are called 

• groups
• periods

Horizontal rows on the periodic table are called ?

• periods
• groups