Inside the Atom We have spent a great deal of time discussing atoms but what do they look like?

3.3 Inside the Atom

• We have spent a great deal of time discussing atoms but what do they look like?

• Atoms are “particles” that are comprised of smaller particles called “subatomic particles”.

• Electrons, protons, and neutrons are subatomic particles.

Inside the Atom - Protons

• Protons are positively charged particles.

• Protons have a relative mass of 1.

• Protons are located in the nucleus of the atom.

• Protons are significant because the number of protons in an atom determines what an atom is.

• For example, any atom with one proton is a hydrogen atom. Any atom with 29 protons is a copper atom.

• The atomic number of an element indicates the number of protons in one atom of that element.

Inside the Atom - Protons

• Identify the element:

• 37 protons

• 48 protons

• 105 protons

Inside the Atom - Protons

• Rubidium

• Cadmium

• Dubnium

Inside the Atom- Electrons

• Electrons are negatively charged particles.

• Electrons have a relative mass of 1/2000 of a proton.

• Electrons travel in regions of space around the nucleus of the atom.

Inside the Atom- Neutrons

• Neutrons are neutral particles.

• Neutrons are neither positively nor negatively charged.

• Like protons, neutrons have a relative mass of 1.

• Like protons, neutrons are found in the nucleus of the atom.

Atomic Number

• The atomic number tells us the number of protons in one atom of the element.

• The atomic number also tells us the number of electrons in one atom of an element.

• The number of electrons is equal to the number of protons when stable.

• Example: the atomic number of calcium is 20 therefore the number of protons is 20 and the number of electrons is also 20.

The Atomic Mass

• The atomic mass tells us the total number of protons and neutrons in one atom of the element.

• Therefore, if we know the atomic number and the atomic mass we can determine the number of neutrons.

• number of neutrons = atomic mass - atomic #

• Example: the atomic number of calcium is 20 and the atomic mass is 40. Therefore, the number of neutrons is 40-20 = 20.

Sample Questions

• For each of the following elements, state the number of protons, electrons and neutrons in one atom.

• Sodium

• Selenium

• Fluorine

• Helium

Sample Questions

• Element Protons Electrons Neutrons

• Sodium 11 11 12

• Selenium 34 34 45

• Fluorine 9 9 10

• Helium 2 2 2

Standard Atomic Notation

• Scientists use a special system to communicate information about any atom.

• This system is known as the standard atomic notation.

• This system represents the numbers of subatomic particles.

• Examples:

• 36Cl 23Na

• 17 11

• The top number is the atomic mass and the bottom number is the atomic number.

Standard Atomic Notation

• 36CL 36 is the atomic mass, 17 is the atomic

• 17 number. The number of protons is 17,

• the number of electrons is 17 and the

• number of neutrons is 19.

• 23Na 23 is the atomic mass, 11 is the atomic

• 11 number. The number of protons is 11,

• the number of electrons is 11 and the

• number of neutrons is 12.

Homework

• Do questions 2 & 3 p.89 (don’t try to look them up on the Periodic table, just use the rules and notes to calculate the answers).