Unit 2 Atomic Structure and Matter Matter and

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 1 oxygen atom (H 2 O)

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?