Notes: Matter Atoms, Periodic Table of Elements, Ions, and Isotopes

Matter 0 Anything that has mass and takes up space. 0 Democritus proposed that all matter is made of small particles we cannot see called atoms. 0 Atoms are the building blocks of matter.

How small is an atom? 0 How small is an atom video How small is an atom video

Structure of the Atom 0 There are two main regions within an atom- 1. Nucleus 0 is located in the center of the atom and it contains protons and neutrons. 0 most of the atom’s mass is located here making it the denser part of the atom. 2. Electron cloud 0 surrounds the nucleus contains electrons. 0 most of an atom’s volume is located in the electron cloud.

Subatomic Particles 0 Protons- 0 Have a positive charge (+) 0 Located inside the nucleus 0 Mass of about 1 amu (atomic mass unit) 0 Neutrons- 0 Have a neutral charge (0) 0 Located inside the nucleus 0 Mass of about 1 amu (atomic mass unit) 0 Electrons- 0 Have a negative charge (-) 0 Located outside the nucleus 0 Mass of about amu (atomic mass unit) 0 So small and contribute very little to the overall mass of the atom.

An Atom’s Charge 0 Atoms have no overall electrical charge and are said to be neutral. 0 The positive charges of the protons are balanced by the negative charges of the electrons. 0 Neutrons are neutral and do not affect the atom’s charge. 0 Neutral atoms have the same number of protons and electrons.

Elements and Atoms 0 An element is a substance that cannot be broken down into other substances by chemical or physical means. 0 An atom is the smallest particle of the element. 0 All elements can be found in an orderly arrangement called the Periodic Table of Elements. 0 The periodic table is a list of all of the elements that can build matter.

Representing Atoms 0 Atoms are so small we cannot see them. So we use models to represent things that are very small and very large. 0 One model used to represent and atom is called the Bohr Model. 0 The Bohr Model shows all of the particles in the atom. 0 In the nucleus are circles. Each circle represents a single neutron or proton. Protons should have a plus (+) or P written on them. Neutrons should be blank, or zero, or have an N. 0 In a circle around the nucleus are the electrons. Electrons should have a minus sign (-) or an e.

Bohr Model

Calculating Sub Atomic Particles 0 Look at your Periodic Table of Elements. 0 The atomic number represents the number of protons in an atom. 0 Since atoms are neutral, the positive charges must equal the negative charges. # of Protons= # of Electrons 0 A tomic # 0 P rotons 0 E lectrons } All three are equal.

Calculating Sub Atomic Particles (cont.) 0 To find the number of neutrons, you must 1. round the atomic mass to the nearest whole number (this number is equal to the number of protons and neutrons in the nucleus) 2. Then subtract the atomic # from the rounded atomic mass to get the number of neutrons in the atom. 0 M ass # (rounded) 0 - A tomic Number 0 = # of N eutrons

Electrons in Bohr Models 0 In a Bohr Model, electrons are shown orbiting the nucleus in set paths called energy levels. 0 Each energy level can hold only a certain number of electrons. 0 The first energy level is located closest to the nucleus and can only hold 2 electrons. 0 The second energy level can only hold 8 electrons. 0 The third energy level can only hold 8 electrons. 0 The electrons located in the outer energy level are called valence electrons.

Drawing a Bohr Model 0 How to draw a Bohr Model! How to draw a Bohr Model!

Created by G.Baker So let’s try it…. 3 Li Lithium Protons = 3 Neutrons = 4 (7-3=4) Electrons = 3 2 in the 1 st shell, 1 in the 2 nd shell

Ions 0 An atom that carries an electrical charge is called an ion 0 If the atom loses electrons, the atom becomes positively charged (because the number of positively charged protons will be more the number of electrons) 0 If the atom gains electrons, the atom becomes negatively charged (because there are more negative charges than positive) 0 The number of protons and neutrons does not change in an ion. 0 So, both the atomic number and the atomic mass remain the same.

Ions This atom has lost an electron. Now it has one more proton than electron. One more proton means one more positive charge. This makes the total charge of the atom POSITIVE. This atom has gained an electron. Now it has one less proton than electron. One less proton means one less positive charge. This makes the total charge of the atom NEGATIVE.

Isotopes 0 The number of protons for a given atom never changes. 0 The number of neutrons can change. 0 Two atoms with different numbers of neutrons are called isotopes. 0 Isotopes have the same atomic #. 0 Isotopes have different atomic Mass # ’ s.

Isotopes