1. Atoms
Chapter 2, Section 1

2. The Building Blocks of Matter
Anything that:
has mass
takes up space

3. The Building Blocks of Matter
Atoms
Tiny particles that make up matter.
Properties of an object are determined by:
the atoms that make up the object
the way in which those atoms join together

4. The Building Blocks of Matter
Elements
Substances that are made up of only one type of atom.
Cannot be broke down into simpler substances by normal chemical or physical means.
There are about 90 naturally occurring elements on Earth.

5. Modeling the Atom Atoms are made of: Protons Neutrons Electrons
Have a positive electrical charge
Neutrons
Have no electrical charge
Electrons
Have a negative electrical charge

6. Modeling the Atom Model by Niels Bohr - 1913 Nucleus
Located at the center of the atom
Contains both protons and neutrons
Electrons travel in orbit-like paths around the nucleus.
Electrons in orbits farther from the nucleus have more energy than electrons in orbits closer to the nucleus.

7. Modeling the Atom Current Model
Electrons are grouped into energy levels.
Each energy level holds a specific number of electrons.
Electrons are located anywhere within an electron cloud that surrounds the nucleus.
Usually located close to the nucleus.

8. Counting Atomic Particles
Atomic Number
Equal to the number of protons in the element.
Moving left to right through the periodic table, the atomic number of each element increases by one.

9. Counting Atomic Particles
Mass Number
Equal to the number of protons plus the number of neutrons.
So, mass number – atomic number = number of neutrons

10. Counting Atomic Particles
How many electrons?
In a neutral atom, the number of protons equals the number of electrons.

11. Counting Atomic Particles
Ions
Atoms of an element that have a charge.
Lose electrons (positive charge)
Gain electrons (negative charge).

12. Counting Atomic Particles
Isotopes
Atoms of the same element that have different numbers of neutrons.

13. Review Number of Protons = Number of Neutrons = Number of Electrons =
Atomic number
Number of Neutrons =
Mass number – number of protons
Number of Electrons =
Number of protons (in a neutral atom)