The Periodic Table

Chapter 17.3

Why is the Periodic Table important to me?

• The periodic table is the most useful tool to a chemist.

• You get to use it on every test.• It organizes lots of information

about all the known elements.• It enable scientists to study

their physical and chemical properties easily

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.

Dmitri Mendeleev: Father of the Table

HOW He WORKED…• Put elements in rows

by increasing atomic mass (check pattern)

• Put elements in columns by the way they reacted.

Periodic table of elements

SOME PROBLEMS…•He left blank spaces for what he said were undiscovered elements. (Turned out he was right!)•He broke the pattern of increasing atomic weight to keep similar reacting elements together.

The Current Periodic Table

• Mendeleev wasn’t too far off.• Henry Mosely later put the elements 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.

Parts of a periodic table

• Visist www.ptable.com and check the parts of the periodic table:

• We have three main parts of the periodic table:- metals, non metals and metalloids.

Metals• Are good conductor of heat and

electricity• Are shiny and sonorous• Are ductile and malleable• Are solid at room temperature

except: mercury which is liquid• Have high melting and boiling

points• Are on the left side of the periodic

table

Non- metals• Are bad conductor of electricity

( with the exception of carbon graphite) and heat.

• Are brittle and dull in appearance• Are generally gases with the

exception of bromine (liquid) and some solids ( carbon, silicon, sulfur…)

• Have low melting and boiling points• Are on the right side of the periodic

table

Metalloids

• Possess some properties of metals and non metals

• They are sometimes called semi metals and are used in semi conductors ( Si and Ge are used in transistors)

• They conduct electric current under very low temperatures.

• Located on the stair line in the periodic table ( check figure at the right)

Periods in a periodic table• Remember that electrons

surround the nucleus, it is very difficult to locate an electron but electrons are mainly found in orbit (also called energy levels shells ). In the nucleus, we have 7 energy levels. Electrons occupy the energy levels close to the nucleus because they have lower energy.

• These energy levels show in the peiodic table as the horizontal rows.

• We have 7 periods in the periodic table.( 7 energy levels)

• The period of an element is the number of shells occupied by electrons in an atom.

Periods in periodic table

• Energy level are usually represented by the letter “n”

• Each energy level ( if n≤4) contains : 2n² electrons.

• For n≥5, check explanation.• Now, calculate the number of

electrons in each shell.

Periodic table of elements:According to this rule: - First shell: 2 electrons- Second shell: 8 electrons- Third shell: 18 electrons- Fourth shell: 32 electrons.However, this is not the case in

the periodic table Why? You will be able to understand this in grade 10 when you learn the concept of suborbits and sublevels.

Groups in the periodic table• Groups in the periodic table

represent the vertical columns. We have 18 groups in the periodic table.

• To understand the concept group, we should know the concept of valence electrons.

• Valence electrons are the electrons present in the outer shell of an atom

Groups…Here’s Where the Periodic Table Gets Useful!!• Elements in the

same group have similar chemical and physical properties!!

• (Mendeleev did that on purpose.)

Why??• They have the same

number of valence electrons.

Families on the Periodic Table

• Columns are also grouped into families.

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

• Families have names rather than numbers. (Just like your family has a common last name.)

Hydrogen

• Hydrogen belongs to a family of its own.

• Hydrogen is a diatomic, reactive gas.

• Hydrogen was involved in the explosion of the Hindenberg.

• Hydrogen is promising as an alternative fuel source for automobiles

Periods in a periodic table

Alkali Metals

• 1st column on the periodic table (Group 1) not including hydrogen.

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

• Soft enough to cut with a butter knife

Alkaline Earth Metals

• Second column on the periodic table. (Group 2)

• Reactive metals that are always combined with nonmetals in nature.

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

Transition Metals

• Elements in groups 3-12• Less reactive harder

metals• Includes metals used in

jewelry and construction.• Metals used “as metal.”

Boron Family

• Elements in group 13• Aluminum metal was

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

Carbon Family • Elements in group 14• Contains elements

important to life and computers.

• Carbon is the basis for an entire branch of chemistry.

• Silicon and Germanium are important semiconductors.

Nitrogen Family• Elements in group 15• Nitrogen makes up over

¾ of the atmosphere.• Nitrogen and phosphorus

are both important in living things.

• Most of the world’s nitrogen is not available to living things.

• The red stuff on the tip of matches is phosphorus.

Oxygen Family or Chalcogens

• Elements in group 16• Oxygen is necessary for

respiration.• Many things that stink,

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

Halogens

• Elements in group 17• Very reactive, volatile,

diatomic, nonmetals• Always found combined

with other element in nature .

• Used as disinfectants and to strengthen teeth.

The Noble Gases

The Noble Gases

• Elements in group 18• VERY unreactive,

monatomic gases• Used in lighted “neon”

signs• Used in blimps to fix the

Hindenberg problem.• Have a full valence shell.

Periodic table of elements

• Use the periodic table : find the group and the period of the 20 first elements. Identify the number of valence electrons for each element.

Periodic Law• PERIODIC LAW, in chemistry, law stating that many of the

physical and chemical properties of the elements tend to recur in a systematic manner with increasing atomic number. Progressing from the lightest to the heaviest atoms, certain properties of the elements approximate those of precursors at regular intervals of 2, 8, 18, and 32. For example, the 2d element (helium) is similar in its chemical behavior to the 10th (neon), as well as to the 18th (argon), the 36th (krypton), the 54th (xenon), and the 86th (radon). The chemical family called the halogens, composed of elements 9 (fluorine), 17 (chlorine), 35 (bromine), 53 (iodine), and 85 (astatine), is an extremely reactive family.

• Watch carefully the video and visit www.ptable.com to compare properties of same group elements.

Electron dot diagram• Electronic configuration:Representation of electrons in

shells around nucleus1. The first shell can fit up to 2

electrons2. The second shell can fit up to 8

electrons3. The third shell can fit up to 8

electrons ( remember not 18 ) 4. Use the periodic table to draw the

electronic configuration of the 20 first elements.

Electron dot diagram

Electron dot diagram• Electron dot structure is a dot

representation of the valence electrons ( remember valence electrons are electrons on the outer shell).

• Electron dot diagrams are used to represent compounds such as H2O( Ch 20)

• Use the blank periodic and your results in slide 33 table to write the electron dot structure of the 20 first elements

Electron dot structure