Chapter 2Elements are the Building Blocks of Matter

ElementsElement: a substance that contains only one kind of

matter and cannot be broken down or separated into simpler substances.

Chemical Symbol: all elements have a chemical symbolOne or two letters, if only one then it is capitalized, but

if two then the first is capitalized and the second is not.These internationally recognized symbols (IUPAC)

create easy communication between scientists of different nations and give a common scientific language.

Twenty Common elementsSymbol is the first letter in name

Symbol is made from two letters in its name

Symbol is based on non-English name

Hydrogen (H) Magnesium (Mg) Sodium (Na)

Carbon (C) Calcium (Ca) Potassium (K)

Nitrogen (N) Nickel (Ni) Iron (Fe)

Oxygen (O) Zinc (Zn) Copper (Cu)

Neon (Ne) Silver (Ag)

Helium (He) Gold (Au)

Chlorine (Cl) Mercury (Hg)

Silicon (Si) Lead (Pb)

Question to consider…What is the difference between Co and CO?

(hint look at the periodic table for help)

Poster Project: Page 45, 2-1C, Essential Elements

Dmitri MendeleevHe organized the known elements at the time

according to their known chemical and physical characteristics

He recognized that spaces needed to be held for elements that had yet to be discovered

He left gaps in his table and suggested that elements would be found to fill these gaps

Mendeleev’s Periodic Table

There are a lot of gaps, but look at the horizontal rows (periods) and compare to the current periodic table.

Current Periodic Table

Periodic Table Periodic table: a chart that organizes all known

elements according to their physical and chemical properties

Most versions include the element’s name, symbol, atomic number and the atomic mass

Atomic Number: equals the number of protons in the nucleus in each atom and …equals the mass of the protons in the nucleus (measured in

atomic mass units, amu)equals the number of electrons in each atom of an element

Atomic mass: the average mass of the atoms in an element. It is written as a decimal and is also measured in amu.

Atomic mass = # of protons + # number of neutrons

OR: Atomic mass = Atomic # + # of neutrons

Complete Activity 2-2A: page 49

Elements are grouped on the basis of similar characteristics

Three major groups formed are: Metals, non-metals and Metalloids

Ductile: ability of a substance to be pulled or stretched

Malleable: ability of a substance to be bent or molded into different shapes

Metals Non-metals Metalloids

ShinyDuctileMalleableConducts heatConducts Electricity

DullNon-ductileNon-malleableDoes not conduct heatDoes not conduct electricity

Shiny or dullNot ductileNot malleablePoor heat conductorMay conduct electricity

Task: Using a blank Periodic Table, we are going to

color code and identify the following parts of the periodic tableMetalsNon-metalsMetalliodsAlkali MetalsAlkaline Earth metalsHalogensNoble gasesTransition Metals

Period: a horizontal row, Number from 1 to 7

Chemical Family or group: a vertical column. The elements in a family or group have similar chemical and physical characteristics. They are numbers 1 to 18.

Website that demonstrates properties and trends of alkali metals and halogens www.teacher s.tv/video/3518

Website with a variety of activities related to the periodic tablewww.nclark.net/PeriodicTable

Families 1: Alkali MetalsAlkali Metals (Column 1)

Very reactive and softReact with water, oxygen and other non-metalsLow melting points Reactivity increases as you move down the

column

Family 2: Alkaline Earth MetalsAlkaline Earth Metals (column 2)

Less reactive than Alkali MetalsBurn in air if heated, produce bright flames

and used in fireworksAlso reacts with waterReactivity increases as you move down the

column

Family 17: HalogensHalogens (Column 17)

Non-metals and highly reactiveFluorine and Chlorine are gases, Bromine is a

liquid and Iodine is a solidReactivity decreases as you move down the

columnAstatine is very rare and little is known about it

Family 18: Noble GasesNoble gases (column 18)

Most stable and unreactive

At room temperature they are colorless and odorless

Some gases, like Argon and Neon are used in light fixtures

Helium is lighter than air and is used in balloons.

Why is Hydrogen special?It occupies a unique position because

sometimes it acts like a metal and sometimes it acts like a non-metal

Sometimes included with alkali metals or with the halogens or off by itself.

Locating Elements on the Periodic Table

Make sure you can identify the relative position of elements on the periodic table

What element is located at period 2, family 3?Boron

Atomic StructureBohr-Rutherford Diagram: shows how many

electrons are in each energy level (electron shell) surrounding the nucleus.

Energy Level (or electron shell): the space around the nucleus in which electrons may be found.Shell closest to the nucleus can hold up to a maximum

of 2 electrons The next two shells can hold up to a maximum of 8

electrons and the fourth shell can hold up to a maximum of 18 electrons.

Known as the 2-8-8-18 pattern

Drawing Bohr-Rutherford DiagramsNeed to be able to draw these diagrams for

the first 18 elementsThese diagrams represent the relative

energies of the atom’s electrons and do not show the position of the electrons in the atom

Electrons do not follow circular paths about the nucleus

The shells should be drawn using horizontal lines NOT CIRCLES.

How to Draw Bohr-Rutherford ModelsStep 1: Draw NucleusStep 2: Put symbol, number of protons and

number of neutrons in the NucleusStep 3: Use the 2-8-8-18 pattern to fill the

energy levels. NOTE: the first energy level is filled first completely before going to the second, the second is filled before going to the third and so on.

See page 62, figure 2.24

Bohr-Rutherford…Valence Energy Level: the energy level that is the

furthest from the nucleus

Valence Electrons: Electrons that are furthest away from the nucleus. They occupy the valence energy level

Valence electrons have higher energies associated with them than those closer to the nucleus

Website to help describe the Bohr atomic modelhttp://videos.howstuffworks.com/hsw/5787-niels-bohrs-

atomic-model-video.htm

Patterns Observed Using Energy Level DiagramsElements in the same family have the same number

of electrons in their valence energy levelPeriod number indicates the number of energy levelsThe valence energy level structure determines how

one element will react with anotherIf the valence level is full, then it is difficult to react

(look at Noble gases)

Website to show the similar properties of elements in families http://videos.howstuffworks.com/hsw/5793-periodic-table-

families-video.htm