Introduction to Atomic Structure

Matter – is anything that takes up space and has mass Mass- is the amount of matter in any object All matter has observable and measurable properties

c. Properties of Matter

i. Chemical properties – characteristics that describe how a substance reacts with other substance to produce a different substance. 1. Requires that scientists have a basic understanding of the particles that make up the substance a. Example: A chemical property of iron is that it will react with oxygen to form rust b. Example: Helium does not react with any other substance Helium atom Formation of Rust

ii. Physical properties – are characteristics that can be observed without changing the composition of a substance. Examples: density (mass / volume) color hardness freezing point boiling point ability to conduct current

II. Elements – a substance that cannot be broken down into simpler substances by chemical means Each element has a characteristic set of physical and chemical properties there are 90 elements that occur naturally on Earth 98% of the earths crust is made up of only 8 elements Every element is represented by a symbol (1 or 2 letters) Organized in a table called the “periodic table of the elements”

III. Atoms- the smallest unit of an element a. Structure: even though atoms are tiny, they are made up of even smaller parts i. Nucleus: Made of protons and neutrons Protons: Particles with a positive charge Neutrons: particles with no charge ii. Electron cloud Electrons: Particles with a negative charge Electron cloud: a region of space that surrounds the nucleus

iii. Atomic number: the number of protons in an atom elements are arranged in the periodic chart by order of their atomic number uncharged atoms have the same number of electrons and protons Number of Protons? 6 28 4 Number of Protons? Number of Protons?

iv. Atomic mass – the sum of the number of protons and neutrons in an atom 1. because an individual atoms has very little mass, weight is given in atomic mass a. atomic mass is the mass (weight) of one mole (6.022 x 10²³) of atoms of any elements # of Protons # of Neutrons Carbon 12 Carbon 13 Carbon 14 6 6 6 7 6 8

v. isotopes – an atom with the same number of protons, but a different number of neutrons I. isotopes have slightly different properties than other atoms of the same element

IV. Valence electrons a. It is believed that electrons orbit the nucleus of an atom in several levels called shells b. the electrons in the outermost level called valence electrons determine the chemical properties of the element

C. The periodic table i. table arranged into columns and rows ii. columns are called groups groups are determined by the number of electrons in the outermost shell elements in the same group can be expected to behave chemically in similar ways The number of valence electrons increases as you move ACROSS the Periodic Table Elements in the same group can be expected to behave chemically in a similar way

iii. Rows are called periods The row number tells you how many energy levels, or shells, the element has. Elements in the period have the same number of rings. The number of rings increases as you move DOWN the Periodic Table Each ring has a maximum number of electrons that can fit on it. Each ring CAN and will hold LESS than the maximum number of electrons. e- e- e- Ring Max Number of e- 1   2 3 e- e- e- e- e- 2 e- e- e- e- N e- e- 8 e- e- e- e- e- e- 16 e- e- e- e- e- e-

Bohr Models  a. First, depending on the atom, figure out its number of rings (energy levels) i. Examples: Hydrogen is on row #1 of the periodic table so it has energy level Next, figure out the atom’s total number of electrons Going in a clockwise direction, fill each energy level with the appropriate number of electrons Period (row) 1 H H H

Bohr Models  a. First, depending on the atom, figure out its number of rings (energy levels) i. Examples: Hydrogen is on row #1 of the periodic table so it has energy level Lithium is on row #2 of the periodic table so it has 2 energy levels. Next, figure out the atom’s total number of electrons Going in a clockwise direction, fill each energy level with the appropriate number of electrons Period (row) 2 Li Li

VI. Lewis Dot Diagrams  Find the valence electron number of the atom (remember that it equals the column or group number). Each valance electron is represented by a dot. Around the atom’s symbol, place the appropriate number of valence electrons Example: Boron Lewis Dot Structure B B Bohr Model