Chapter 5The Periodic Table

Key Concepts:·         Mendeleev arranged the elements into rows in order of increasing mass so that elements with similar properties were in the same column.·         The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be.

5.1 Organizing the Elements:

Why is the Periodic Table important to me?

The periodic table is the most useful tool in chemistry.

You get to use it on quizzes and tests!

It organizes lots of information about all the known elements.

Pre-Periodic Table Chemistry …

…was a mess!!!No organization of

elements.Imagine going to a grocery

store with no organization!!Difficult to find information.Chemistry didn’t make

sense.

Previous attempts to organize known elements failed to work for all known elements at the time

Russian Chemist and teacher, Dmitri Mendeleev, discovered a way

Found a way to approach the problem when playing his favorite card game, a version of solitaire (organization was the key)

Solitaire…??????

Dmitri Mendeleev: Father of the Table

How does the game of solitaire work???

HOW HIS WORKED…Put elements in rows by increasing atomic

weight.Elements with similar properties were in the

same column.Put elements in columns by the way they

reacted.

Dmitri Mendeleev: Father of the Table

Periodic Table: an arrangement of elements in columns, based on a set of properties that repeat from row to row

Mendeleev’s Periodic Table

Table was not complete, not all elements had yet been discovered

He left gaps/spaces in his table for those elementsHe was NOT the first to organize the elements in

the form of a tableHe was the FIRST to offer good explanations for

how the properties of an element were related to its location in his table

He used the gaps in his tables to predict properties of undiscovered elements

Other scientists used the predictions to help in their search for undiscovered elements

Mendeleev’s Prediction

The close match between Mendeleev’s predictions and the actual properties of new elements showed how useful his periodic table could be

With the periodic table, chemists could do more than predict the properties of new elements – they could explain the chemical behavior of different groups of elements!!!

Evidence Supporting Mendeleev’s Table

5.2 The Modern Periodic Table

Mendeleev wasn’t too far off.Now the elements are put in rows by

increasing ATOMIC NUMBER!!

The horizontal rows are called periods and are labeled from 1 to 7.

The vertical columns are called groups are labeled from 1 to 18.

The Current Periodic Table

Period: A row in a periodic table of elements (left to right)

To understand the structure of the table, think what happens as the atomic number increases: Reminder: Atomic Number = Number of Protons

First energy level has ONLY 1 orbitalThe 1 e- in a hydrogen atom and 2 e- in a

helium atom can fit in this orbital (first energy level)

This is why H and He are in Period 1

PERIODS

Lithium, 1st element in Period 2, has one of its the three electrons in the second energy level This is why lithium is the first element in

Period 2Sodium, 1st element in Period 3, has one e- in

its third energy levelPotassium, 1st element in Period 4, has 1 e- in

its fourth energy levelThis pattern applies to ALL the elements in

the 1st column on the table 

PERIODS

Families (groups) on the Periodic Table

Columns are also grouped into families (or groups).

Families may be one column, or several columns put together.

Families have names (Just like your family has a common last name.)

Group: A column in a periodic table of elements

Properties of elements repeat in a predictable way when atomic numbers are used to arrange elements into groups

Groups

Periodic Law: the pattern of repeating properties displayed by elements in the periodic table

Elements within a group have similar properties: Similar e- configurations (see example

above – first column of the table) Electron configuration determines an

elements chemical properties

Groups

Various Trends of the Periodic Table

Atomic mass is a value that depends on the distribution of an element’s isotopes in nature and the masses of those isotopes.

Atomic Mass

Mass of an atom in grams is EXTREMELY small

Scientists came up with an easier way to talk about mass Chose one isotope to serve as a standardScientists assigned 12 atomic mass units

(amu’s) to the carbon-12 atom (which has 6P and 6N)

Atomic Mass Unit (amu): 1/12 the mass of a carbon-12 atom

Atomic Mass Units

Chlorine has an atomic number of 17 and an atomic mass of 35.453 atomic mass units

Where does the number 35.453 come from??? There are two natural isotopes of Chlorine:

Chlorine-35 which has 17 protons and 18 neutrons

Chlorine-37 which has 17 protons and 20 neutrons

An Example…Isotopes of Chlorine

Atomic masses come from an average of the isotopes for a given element that exist in nature

The value for atomic mass is known as a “weighted average”

Cl-35 occurs 3 times as often as Cl-37

Take an average of those numbers: (3 × 35) + (1 × 37) ----------------------------- = 35.453 4

It’s a weighted average of the isotopes

Elements are classified as metals, nonmetals, and metalloids.

Classes of Elements

Metals

Metals: elements that are good conductors of electric current and heat.

Properties of Metals:Except for mercury, metals are solid at room

temperatureMost metals are malleableMany metals are ductile (can be drawn into thin

wires)Some metals are extremely reactive* (page

135, figure 10)*Meaning they easily combine chemically with

other elements

Metals

Transition Metals: metals in groups 3-12, form a bridge between the elements on the left and right sides of the tables. Examples: copper and silverSome of the first elements discovered Ability to form compounds with distinctive

colors (page 137 production of colored glass)

Includes the lanthanide and actinide series (at the bottom of the table)

Transition Metals

Nonmetals

Nonmetals: elements that are poor conductors of heat and electric current Properties opposite those of metals

Low boiling pointsMost are gases at room temperatureNonmetals that are solid at room

temperature tend to be brittle (will shatter)Some very reactive, some not at all, some

fall somewhere in betweenFluorine (in Group 17) is the most reactive

nonmetal (found in toothpaste)

Nonmetals

Metalloids

Metalloids: elements with properties that fall between those of metals and nonmetals Ability to conduct electric current varies

with temperature Pure silicon (Si) and germanium (Ge) are

good insulators at low temperatures and good conductors at high temps.

Metalloids

Across a period from left to right, the elements become less metallic and more nonmetallic in their properties Most reactive metals on left side Most reactive nonmetals on the right side (in

Group 17) Period 3 elements (left to right) provide an

example of this (page 138, Figure 13)

Variation Across a Period

5.3 Representative Groups

Why is hydrogen (H) on the left side of the table with the active metals?

Hydrogen’s location is related to its electron configuration, not its properties!!!

Hydrogen…

Wonder why there are 2 numbering schemes on the periodic table?When the ‘A’ groups are numbered 1-8, they

provide a reminder about the electron configurations of the elements in those groups

The number of an ‘A’ group matches the number of valance electrons in an electron configuration for an element in that group

Patterns of Electron Configuration

Valence Electron: an electron that is in the highest occupied energy level of an atomValence electrons play a key role in chemical

reactionsProperties vary across a period because the

number of valence electrons increases from left to right

Elements in a group have similar properties because they have the same number of valence electron

Hydrogen is on far left of table because it has one valence electron, just like the rest of the elements in that column

Valence Electrons

Valence Electrons

Valence Electrons Lewis Structure

Hydrogen- YellowHydrogen belongs to

a family of its own.Hydrogen is a

diatomic, reactive gas.

Hydrogen was involved in the explosion of the Hindenberg.

http://www.youtube.com/watch?v=F54rqDh2mWA

Hydrogen is promising as an alternative fuel source for automobiles.

Alkali Metals- Lt. Blue1st column on the periodic table

(Group 1 /1A) not including hydrogen.

Very reactive metals, always combined with something else in nature (like in salt).

Single valence electronSoft enough to cut with a butter knife.The reactivity of alkali metals increases

from the top of Group 1A to the bottomLithium (Li) down through Francium (Fr)

http://www.youtube.com/watch?v=m55kgyApYrY

Alkali Metals

Alkaline Earth Metals- BrownGroup 2 / 2A on the periodic

table. Reactive metals that are

always combined with nonmetals in nature.

Several of these elements are important mineral nutrients (such as Mg and Ca).

2 valence electronsHarder than metals in Group 1AHigher melting point than Group 1ADifferences in reactivity among the

alkaline earth metals are shown by the ways they react with waterCalcium, strontium, and barium react easily

with cold waterMagnesium reacts with hot waterNo change with beryllium and water

Alkaline Earth Metals

Transition Metals- WhiteElements in

groups 3-12Less reactive,

harder metals.Includes metals

used in jewelry and construction.

Most are hard and shiny.

Transition Metals- White

Boron Family- Light GreenElements in group 13 (3A)Aluminum:

Metal was once rare and expensive, not a “disposable metal.”

Most abundant metal in Earth’s crust

Less reactive than sodium and magnesium

strong, lightweight, malleable, and good conductor of electric current

3 valence electronsBoron is used in

glassware like flasks because it doesn’t shatter when it undergoes a rapid temperature change

Boron Family

Carbon Family- RedElements in group 14 (4A)Group 4A contains one nonmetal (C), 2

metalloids (Si, Ge), and 2 metals (Sn, Pb)

Contains elements important to life and computers.

Carbon is the basis for an entire branch of chemistry.

Coal and oil are mostly made of carbon.

4 valence electronsMetallic nature increases from top to

bottom (Ge is better conductor than Si)Life would not exist without carbon (except

for water, most of the compounds in your body contain carbon)

Reactions in your body controlled by carbon compounds

Si is 2nd most abundant element in Earth’s crust (found in rocks, sand, and glass)

Carbon Family

Nitrogen Family- Dark BlueElements in group 15 (5A)Nitrogen makes up over ¾ of

the atmosphere.Nitrogen and phosphorus are

both important in living things.

The red stuff on the tip of matches is phosphorus.

5 valence electrons2 nonmetals, 2

metalloids, and 1 metal

Contain a wide range of physical properties

Nitrogen Family

Oxygen Family- Orange

Elements in group 16 (6A)Oxygen is necessary for

respiration.Many things that stink, contain

sulfur (rotten eggs, garlic, skunks, etc.)

6 valence electrons3 nonmetals and 2 metalloidsOxygen is most abundant element in

Earth’s crust

Oxygen Family

The 10 most abundant elements by mass in the earth's crust . All are main-group elements except iron and titanium.

Halogens- PurpleElements in group 17 (7A)Very reactive, volatile, diatomic,

nonmetalsAlways found combined with

other element in nature .Used as disinfectants and to

strengthen teeth.

7 valence electronsDespite physical differences, the halogens

have similar chemical propertiesHighly reactive nonmetals, with fluorine being

the most reactive and chlorine a close 2nd

React easily with most metalsChlorine added to drinking water and

swimming pools to kill bacteria

The Halogens

The Noble Gases- Dark GreenElements in group 18

(8A)VERY unreactive,

monatomic gasesUsed in blimps to fix the

Hindenberg problem.Have a full valence

shell.

8 valence electronsEXCEPTION is Helium, it has 2 valence

electronsColorless and odorlessUsed in lighted “neon” signs

The Noble Gases