Chemical Building Blocks Chapter 3 Elements and the Periodic Table

SECTION 1 INTRODUCTION TO ATOMS

Structure of an Atom The center core of an atom is called ________. Inside that core, you will find ________ and _______. _______ have a positive electric charge (+) _______ have a no charge. ___________ move rapidly around the core of an atom. They have a negative electric charge (-).

Atom

John Dalton’s Model - 1808 Each element is made of atoms that are all alike. But each element has different sized atoms. Atoms are like tiny solid spheres.

Thomson Model - 1897 Positively charged atom with electrons embedded in it (kind of like a raisin muffin)

Rutherford Model - 1911 His experiments led him to conclude that most of the mass of the atom is the nucleus. Most of the atom is empty space. Electrons orbit the nucleus.

Bohr Model - 1913 He concluded that electrons orbit the nucleus in specific layers called “shells”. There is a change in energy when electrons move from one “shell” to another. http://www.colorado.edu/physics/2000/quantumzone/bohr.html

Present Modern Model Electrons form a negatively charged cloud around the nucleus and it is impossible to determine exactly where an electron is at a given time

Electrons w/ lower energy move closer to nucleus. Electrons w/ higher energy move farther from the nucleus Most of atom’s volume is taken up by electrons Most of atom’s mass is taken up by protons and neutrons

Protons and neutrons are ~ the same mass. About 2000 electrons = mass of 1 proton. http://www.phrenopolis.com/perspective/atom/

Modeling Atoms Scientists can get an idea about atoms by using microscopes but they cannot see the structure of atoms or how they might work. Rather, scientists create models to describe atoms. Atoms are amazingly small. The smallest visible speck of dust may contain 10 million billion atoms. Even a sheet of paper is about a million atoms thick.

Mass of an atom Atoms are SOOOO small that it doesn’t make sense to measure their mass is everyday measurements. Instead, scientists use AMU (atomic mass units) 1 atomic mass unit = 1.66053886 × 10-27 kilograms 1 proton’s mass = 1 amu 1 neutron’s mass = 1 amu 1 electron’s mass = _________amu

http://www.nature.com/news/2010/100707/full/news.2010.337.html

Atoms and Elements

Atomic Number

http://www.youtube.com/watch?v=d0zION8xjbM

Atoms and Elements The periodic table is composed of elements. Elements are the basic building blocks of matter. All elements are made of atoms. All atoms are made of protons, neutrons and electrons. Elements are identified by the number of protons in the nucleus of their atoms.

Protons Elements are made of __________. Every single atom of an element has the same number of _________. Atomic Number = number of protons in nucleus

NEUTRONS The number of neutrons in atoms of an element can vary. Isotopes = atoms with the same number of protons and different number of neutrons

Mass Number The sum of the protons and neutrons in the nucleus of an atom. Why do you think it does not include the mass of the electrons?