Unit 2 Atomic Structure and Matter

Matter and Atoms Matter describes anything that has mass and volume Can matter be invisible? YES Ex. Air

History of atoms Democritus Was a Greek philosopher in 400 BC Thought the universe was made of atoms and empty space ATOM comes from the Greek word atomos, which means cannot be divided

Antoine Lavoisier Was a French chemist in the late 1700’s Lavoisier proved that matter cannot be created or destroyed during chemical changes like burning or rusting The principle is called The Law of Conservation of Matter

Joseph Proust Was a French chemist He stated that the basic building blocks of a substance are always in the same way For example every molecule of water is made of 2 hydrogen atoms and 1oxygen atom (H2O)

Models of the Atom What is a model? A model is anything that lets you create an image in your mind of something that is too big, too small or too complex to understand otherwise Models can also be used to study events that happen too fast or too slow or would be too dangerous to study otherwise

John Dalton’s Atomic Model Dalton was an English chemist In 1803, he proposed that atoms of the same element are the same and atoms of different elements are different For example, a piece of lead is made up of only lead atoms He also stated that atoms are the smallest particle of matter.

Atomic Models Atoms are too small to see with the human eye We need models to help us understand what they look like Models are not completely accurate. They represent something that is not easily seen or understood

Atomic Structure The Nucleus Is the center of the atom 99.9% of an atom’s mass is in the nucleus The nucleus is made of protons and neutrons Protons have a positive charge Neutrons have no charge What charge does the nucleus have? Positive

The Electron Cloud Around the nucleus the electrons fly around in random patterns An electron has an negative charge An atom has equal numbers of protons and electrons

Electron Cloud An electron is about 1800 times lighter than a proton or a neutron Electrons can easily be lost because they are far away from the nucleus. Have you ever rubbed a balloon on your head? Have you ever zapped your little brother?