Atoms Chapter 2, Section 1

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

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

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.

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

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.

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.

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.

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

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

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

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

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)