elements

Elements

An element is either classified as a metal, nonmetal or metalloid.

The classification depends on the elements location on the periodic table.

Metals are in pink. Nonmetals are in lime green.

B

Si

As

Sb Te

Po At

Metalloids are in white.

Ge

1 2 3 4 5 6 7

Metals are in yellow.

Elements

1 2 3 4 5 6 7

Nonmetals are in purple.

Elements

1 2 3 4 5 6 7

Metalloids are in green.

Elements

Properties of Metals

Metals are elements that have luster, conduct heat and electricity, and usually bend without breaking.

Metals are also ductile (can be drawn out into a wire).

All metals except mercury (Hg) are solids at room temperature; in fact, most have extremely high melting points and high boiling points.


A metal’s reactivity is its ability to react with another substance.

Metals in the first and second column of the periodic table are more reactive than other metals.


Although the majority of the elements in the periodic table are metals, many nonmetals are abundant in nature.

Properties of Nonmetals

Most nonmetals don’t conduct electricity, are much poorer conductors of heat than metals, and are brittle when solid.

Many are gases at room temperature; those that are solids lack the luster of metals.


Their melting points tend to be lower than those of metals.

Fluorine is the most reactive nonmetal.


Metalloids have some chemical and physical properties of metals and other properties of nonmetals.

In the periodic table, the metalloids lie along the border between metals and nonmetals.

Properties of Metalloids

Some metalloids such as silicon, germanium (Ge), and arsenic (As) are semiconductors.

A semiconductor is an element that does not conduct electricity as well as a metal, but does conduct slightly better than a nonmetal.


Objectives

PSc.2.1.4– Interpret the data presented in

the Bohr model diagrams and dot diagrams for atoms and ions of elements 1 through 18.

Modern View of the Atom

The atom has two regions and is 3-dimensional.

The nucleus is at the center and contains the protons and neutrons.

The electron cloud is the region where you might find an electron and most of the volume of an atom.

Modern View of the Atom

Subatomic Particles

Electron

Proton

Neutron

Name Symbol ChargeRelative mass

e-

p+

n0

-1

+1

0

1/2000

1

1

Symbol ChargeRelative mass

Atomic Number

The atomic number of an element is the number of protons in the nucleus of an atom of that element.

The number of protons determines identity of an element, as well as many of its chemical and physical properties.

Mass Number

The sum of the protons and neutrons in the nucleus is the mass number of that particular atom.

Symbols

Elements can be represented by using the symbol of the element, the mass number and the atomic number.

X Mass

number

Atomicnumber

The mass number is the atomic mass rounded to a whole number.

Problem

Determine the following for the fluorine atom depicted below.

F19 9

e) mass number

d) atomic number

c) number of electrons

b) number of neutrons

(9)(10)

(9)

(9)(19)

a) number of protons

Problem

Determine the following for the bromine atom depicted below.

Br80 35

e) mass number

d) atomic number



(35)(45)

(35)

(35)(80)


Problem

Se78 34d) complete symbol



(34)(44)(34)


If an element has an atomic number of 34 and a mass number of 78 what is the

Problem

Pa231 91d) complete symbol


b) mass number

(91)

(140)(91)

a) atomic number

If an element has 91 protons and 140 neutrons what is the

Cations

A cation is a positive ion. It is formed when an atom loses one or

more electrons.

Ca2+

Anions

An anion is a negative ion. It is formed when an atom gains one or

more electrons.

Cl1-

Problem

Determine the following for the chlorine ion depicted below.

Cl1-35 17

e) atomic number

d) mass number

c) number of protons

b) number of electrons

(18)(18)

(17)

(35)(17)

a) number of neutrons

Problem

Determine the following for the aluminum ion depicted below.

Al3+27 13

e) number of neutrons

d) number of protons

c) atomic number

b) number of electrons

(27)(10)

(13)

(13)(14)

a) mass number

In 1910, J.J. Thomson discovered that neon consisted of atoms of two different masses.

Isotopes

Atoms of an element that are chemically alike but differ in mass are called isotopes of the element.

Isotopes

Consider the isotope of carbon that has a mass number of 14. The following are different ways to write symbols for this isotope.

Isotopic Notation

Carbon-14

C-14

14C

14C 6

The Bohr Model of the Atom

Niels Bohr, a young Danish physicist working in Rutherford’s laboratory in 1913, suggested that the single electron in a hydrogen atom moves around the nucleus in only certain allowed circular orbits.

The atom looked like a miniature solar system.

The nucleus is represented by the sun, and the electrons act like the planets.


Nucleus

Electron

Orbit

Energy Levels


The orbits are circular and are at different levels.

Amounts of energy separate one level from another.


Bohr Diagrams

1) Find your element on the periodic table.

2) Determine the number of electrons 3) This is how many electrons you will

draw.

Find out which period (row) your element is in.

Elements in the 1st period have one energy level.

Elements in the 2nd period have two energy levels, and so on.

Bohr Diagrams

1) Draw a nucleus with the element symbol inside.

2) Carbon is in the 2nd period, so it has two energy levels, or shells.

3) Draw the shells around the nucleus.

Bohr Diagrams

C

1) Add the electrons.

2) Carbon has 6 electrons.

3) The first shell can only hold 2 electrons.

Bohr Diagrams

C

1) The second shell can only hold 8 electrons.

2) The third shell can only hold 18 electrons.

Bohr Diagrams

C

1) Since you have 2 electrons already drawn, you need to add 4 more.

2) These go in the 2nd shell.

3) Add one at a time -starting on the right side and going counter-clockwise.

C

Bohr Diagrams

Try the following elements on your own:

a) H b) Hec) O2-

d) Mg2+

e) Nef) Ar

Bohr Diagrams


a) H b) Hec) O2-

d) Mg2+

e) Nef) Ar

H

Bohr Diagrams

1 electron


a) Hb) Hec) O2-

d) Mg2+

e) Nef) Ar

He

Bohr Diagrams

2 electrons


a) Hb) Hec) O2-

d) Mg2+

e) Nef) Ar

Bohr Diagrams

O2-

10 electrons


a) Hb) Hec) O2-

d) Mg2+

e) Nef) Ar

Bohr Diagrams

Mg2+

10 electrons


a) H b) Hec) O2-

d) Mg2+

e) Ne f) Ar

Bohr Diagrams

Ne

10 electrons


a) H b) Hec) O2-

d) Mg2+

e) Nef) Ar

Ar

Bohr Diagrams

18 electrons

Electron Dot Diagrams

♦ An electron dot diagram illustrates valence electrons as dots (or other small symbols) around the chemical symbol of an element.

♦ Each dot represents one valence electron.

♦ In the dot diagram, the element’s symbol represents the core of the atom—the nucleus plus all the inner electrons.


Write the symbol.

X♦ Put one dot for each valence electron.

♦ Don’t pair electrons up until you have to.


Write a Lewis dot diagram for chlorine.


Write a Lewis dot diagram for calcium.


Write a Lewis dot diagram for potassium.


CHEMICAL BONDING and CHEMICAL INTERACTIONS

PSc.2.2 OBJECTIVE: Understand chemical bonding and chemical

interactions.

Objectives PSc.2.2.1

–Infer valence electrons, oxidation number, and reactivity of an element based on its location on the Periodic Table.

Bonding and Molecules

The outer electrons are involved in bonding.

These are called valence electrons.

Bonding and Molecules Most stable

atoms have eight valence electrons.

When an atom has 8 valence electrons, it is said to have an octet of electrons.

The Octet Rule

Oxidation Number An oxidation

number indicates how many electrons are lost, gained, or shared when bonding occurs.

1A

2A 3A 4A 5A 6A7A

8A0

The elements in the A groups are called the representative elements.

1A Group 1A elements have one valence electron.

They form 1+ ions after losing the one valence electron.

1+ is referred to as the oxidation number for Group 1A elements.

2A Group 2A elements have two

valence electrons. They form 2+ ions after losing the

2 valence electrons. 2+ is referred to as the oxidation

number for Group 2A elements.

3A

Group 3A elements have three valence electrons.

They form 3+ ions after losing the 3 valence electrons.

3+ is referred to as the oxidation number for Group 3A elements.

4A

Group 4A elements have four valence electrons.

They form 4+ ions after losing the 4 valence electrons.

They could just as easily form 4- ions after gaining four additional electrons.

4A

Group 4A elements could have a 4+ or 4- oxidation number, depending on the element with which they are bonding.

Group 4A

Two elements in Group 4A have multiple oxidation numbers of 2+ and 4+.

These two elements are tin (Sn) and lead (Pb).

5A

Group 5A elements have five valence electrons.

They form 3- ions after gaining 3 additional electrons.

3- is referred to as the oxidation number for Group 5A elements.

6A

Group 6A elements have six valence electrons.

They form 2- ions after gaining 2 additional electrons.


7A

Group 7A elements have seven valence electrons.

They form 1- ions after gaining 1 additional electron.


8A Group 8A elements have eight

valence electrons, except helium which only has 2.

Group 8A elements, with a full complement of valence electrons, are generally not reactive.

Question

How many valence electrons are in an atom of each of the following elements?

a) Magnesium (Mg)

b) Selenium (Se)

c) Tin (Sn)

(2)

(6)

(4)

Question

Determine the oxidation number of each of the following elements.

a) Potassium (K)

b) Chlorine (Cl)

c) Tin (IV) (Sn)

(1+)

(1-)

(4+)

Reactivity of Metals

In general, the reactivity of metals increases from top to bottom and decreases from left to right.

Reactivity of Metals

Reactivity of Nonmetals

In general, the reactivity of nonmetals increases from left to right and decreases from top to bottom.

elements

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