The Periodic Table Physical Science Unit 8

Part 1: Periodic Table

Early Tables Antoine Lavoisier – late 1700’s Compiled a list of all known elements at the time and placed them into four categories Dimitri Mendeleev – late 1800’s Demonstrated a connection between atomic mass and elemental properties Ordered by increasing atomic mass Into columns with similar properties Left blank spaces for where he thought undiscovered elements would be placed Henry Moseley - 1913 Ordered elements based on Atomic Number (number of protons)

Mendeleev’s Table

Periodic Law States that there is a periodic (recurring) pattern of chemical and physical properties of the elements when they are arranged by increasing atomic number (number of protons)

Modern Periodic Table Consists of boxes typically containing Element name Symbol Atomic number Atomic mass Boxes arranged in order of increasing atomic number with Series of columns called groups or families Series of rows called periods

Atomic Mass Mass of the atom is mostly a result of the protons and neutrons in the nucleus. Electrons weigh almost nothing Unit of measurement is called the atomic mass unit or amu 1 amu is equal to 1/12 the mass of a carbon-12 atom

Average Atomic Mass The mass of an element is determined by taking the average mass of all the isotopes of that element. It is this average mass that is used as the amu for the element on the periodic table

Why the Weird Shape? Elements are not only in numerical order of protons, but also grouped by characteristics and properties of elements

Columns and Rows Groups – the vertical columns of the periodic table Representative elements in group have same number of outer electrons All elements in group have similar properties Periods – the horizontal rows of the periodic table Rows indicate energy level of an atom’s electrons

Basic Structure 7 periods beginning with hydrogen 18 groups Representative Elements – often called the “main group” and contains groups 1,2, and 13-18 Transition Elements – (in the center) containing groups 3 to 12 Element Classification – classified as metals, non-metals or metalloids

Types of Elements Metals – left side Metalloids – in between Non-metals - right side

Metals Characteristics – Most are malleable and ductile 1. shiny (when smooth and clean) 2. solid at room temperature 3. good conductors of heat and electricity 4. high mp and bp Most are malleable and ductile Most elements are metals

Types of Metals Alkali Metals – group 1 elements (except for hydrogen) Very reactive Usually exist as compounds with other elements Alkaline Earth Metals – group 2 Transition Metals – groups 3-12 Inner Transition Metals – 2 rows at the bottom of table called the lanthanide series and the actinide series

Non-Metals Occupy the upper right side of the periodic table Low melting and boiling points Generally gases or brittle, dull-looking solids The only liquid at room temperature is bromine

Groups of Non-Metals Halogens – group 17 Noble Gases - group 18 highly reactive and often found in compounds with other elements Noble Gases - group 18 Very stable unreactive

Metalloids Elements bordering the stair step line Have chemical and physical properties of both metals and non-metals

Electrons and the Periodic Table Part 2: Electrons and the Periodic Table

Electrons in Atoms Can use periodic table to determine number and position of electrons How? Each row tells you what energy shell or level you are in. Energy level one has up to 2 electrons Energy level two has up to 8 electrons In a neutral atom, there are the same number of protons as electrons

Valence Electrons Use the periodic table to determine the number of outer level electrons Outer level electrons are called valence electrons Group number on periodic table tells you number of valence electrons Number of valence electrons determines the chemical behavior of an element

Group number – 1 2 13 14 15 16 17 18 # of valence 1 2 3 4 5 6 7 8 electrons

Lewis Dot Structure Use group number to determine number of valence electrons – also called electron dot Write chemical symbol then add dots one at a time up to 8 total Ex Fluorine In group 17 – so 7 valence e- Chemical symbol – F Dot structure F

Octet Rule Most atoms are always trying through reactions to achieve a full set of 8 electrons in their outermost energy level. Bohr model doesn’t explain this, so we will delve a little bit into the quantum mechanical model to explain why this is so.

Magic Number “8” Why 8? (remember energy level 3 with 18 e-?) Energy levels don’t fill in sequential order. The energy level have sections called orbitals Think of it like a theater having sections and each section has rows – ex. Balcony section: Row s That is how electrons work too These rows or orbitals are called s, p, d, f They are represented in blocks on the periodic table For any element beyond He on the table, the highest energy level electrons in any one particle period will be no more than 8 explaining the octet rule Total number of electrons in lower energy levels can achieve their regular amounts (2, 8, 18, 32)

Let’s Take a Closer Look d-block electrons are always one energy level lower than the s and p in the same period. so valence electrons are the total of s and p electrons.

Energy Levels and Orbitals Only s Energy level 2 – s and p Energy level 3 – s, p, d Energy level 4 – s, p, d, f nucleus

Actual Shapes Actual shapes look like this around the nucleus

Common Ion Charges Because of this, we can use the group numbers along with the octet rule to determine what ion an atom is likely to form for many of the representative elements Group 1 (alkali metals) – have 1 valence e- They want to lose this one and go down to the lower level that is full so form 1+ ions Group 2 (alkaline earth metals) – have 2 valence e- They want to lose these two and go down to the lower level that is full so form 2+ ions Group 17 (halogens) – have 7 valence e- They want to gain one more electron and fill their outer level and so form 1- ions

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