1.2 Formation of Ions 1.3 Periodic Table. Recall from Previous Lesson.

1.2 Formation of Ions1.3 Periodic Table

Recall from Previous Lesson

Refer to page 9 of your notes

Formation of Ions

1. During chemical reactions, some atoms might lose/gain electron(s).

2. Atom becomes an ion (charged particle) when it gains or loses electron(s).

Question: Why does an atom become a charged particle when it gains or loses electron(s)?

•An atom is electrically neutral because number of

electrons = number of protons (equal positive and negative

charges).

•When it gains or loses electron(s), the positive and

negative charges are not balanced.

•Therefore, the atom becomes a charged particle.

(positively charged or negatively charged)



Formation of Cations

When an atom loses one or more electrons, it becomes a positively charged particle called cation.

Lithium atom (Li)3 electrons3 protonsNet charge: 0

Lithium ion (Li+)2 electrons3 protonsNet charge: +1

In a lithium atom, there are 3 protons and 3 electrons.

In a lithium ion, there are 3 protons and 2 electrons.

Therefore, the lithium ion carries an overall positive charge of 1+ and is written as Li+.

Metal Chemical Symbol

Proton Number

Electronic Configuration

Gain/Lose Electrons

Name of Ion Formula of Ion

Sodium Na 11 (2,8,1) Lose 1 electron Sodium ion Na+

Magnesium Mg 12 (2,8,2) Lose 2 electrons Magnesium ion Mg2+

Aluminum Al 13 (2,8,3) Lose 3 electrons Aluminum ion Al3+

Metals form positively charged ions (cations).

More examples of Ions of some Metals



Formation of Anions When an atom gains one or more electrons, it becomes a negatively charged particle called anion.

Fluorine atom (F)9 electrons9 protonsNet charge: 0

Fluoride ion (F-)10 electrons9 protonsNet charge: -1


In a fluorine atom, there are 9 protons and 9 electrons.

In a fluoride ion, there are 9 protons and 10 electrons.

Therefore, the fluoride ion carries an overall positive charge of 1- and is written as F-.

Non-metals form negatively charged ions (anions).

Metal Chemical Symbol

Proton Number

Electronic Configuration

Gain/Lose Electrons

Name of Ion Formula of Ion

Chlorine Cl 17 (2,8,7) Gain 1 electron Chloride ion Cl-

Oxygen O 8 (2,6) Gain 2 electrons Oxide ion O2-

Sulphur S 16 (2,8,6) Gain2 electrons Sulphide ion S2-

More Examples of Ions of some Non-metals

Thinking Time (page 10)

Why do atoms become ions?

(Note: this will be covered under chemical bonding)

•To obtain a full valence shell (based on observation

from above example).

•To obtain the same electronic structure of a noble gas

so as to be stable


Recall: An element is a pure substance that cannot be split up into two or more simpler substances.

History of the Periodic Table

During the 19th century, several chemists looked for patterns in the properties of elements.

The most successful of these approaches was by the Russian chemist Dmitri Mendeleev in 1869.

Mendeleev arranged all the known elements in order of their relative atomic masses.

He also arranged the elements in horizontal rows so that elements with similar properties were in the same vertical column.


He left gaps in his table so that similar elements were in the same vertical group. Three of these gaps are shown as asterisks in the figure above.


1. He predicted the properties of the missing elements from

the properties of elements above and below them in his

table.

2. Within 15 years of his predictions, the missing elements

had been discovered. They were called scandium,

gallium and germanium.

3. Their properties were very similar to Mendeleev's

predictions.

Refer to page 12 of your notes The names of elements are represented by chemical symbols.

For example, carbon is represented by ‘C’ and chlorine is represented by ‘Cl’.

Elements that are arranged in the same horizontal row belong to the same period. (same number of electrons shells) Each element in a period has a proton number which is one less than the element after it. As, we move gradually from left to right, the properties of the elements gradually change from metals to non-metals.

Elements that are arranged in the same vertical column belong to the same group. Elements in the same group have the same chemical properties. There are 8 groups of elements from Group I to Group 0.

Divides metal from non-metals. Elements found along this line are known as metalloids. They have some properties of metals and non-metals.


Group number Group

I Alkali metals

II Alkaline earth metals

VII Halogens

0 Noble gases

(a) Group

The groups in the Periodic Table are numbered from I to VII and then Group 0. Some of these groups have names:1. Elements between Group II and III are known as transition metals or

transition elements. 2. Elements in the same group have similar chemical properties and

will undergo the same type of chemical reactions.


(b) Period

Each period is numbered, 1, 2, 3, etc.

Elements in the 1st period will only have their 1st shell fully/partially occupied with electrons.

Elements in the 2nd period will have their 1st shell fully occupied with electrons, and their 2nd shell fully/partially occupied with electrons.


Element Proton number

Number of electrons in Electronic configuration

Period Group 1st shell 2nd shell 3rd shell

4th shell

H 1 1 1 1 -He 2 2 2 1 0 Li 3 2 1 2.1 2 I Be 4 2 2 2.2 2 II B 5 2 3 2.3 2 III C 6 2 4 2.4 2 IV N 7 2 5 2.5 2 V O 8 2 6 2.6 2 VI F 9 2 7 2.7 2 VII

Ne 10 2 8 2.8 2 0 Na 11 2 8 1 2.8.1 3 I Mg 12 2 8 2 2.8.2 3 II Al 13 2 8 3 2.8.3 3 III Si 14 2 8 4 2.8.4 3 IV P 15 2 8 5 2.8.5 3 V S 16 2 8 6 2.8.6 3 VI Cl 17 2 8 7 2.8.7 3 VII Ar 18 2 8 8 2.8.8 3 0 K 19 2 8 8 1 2.8.8.1 4 I Ca 20 2 8 8 2 2.8.8.2 4 II

Refer to supplementary notes

Group 1 Elements – Alkali Metals

1. The elements in Group 1 are known as alkali metals because they react with water to form alkalis.

2. They are reactive metals and are stored in oil to prevent them from reacting with water and air.

Alkali Metals

Electronic Structure

1) One Electron on the

outer most shell2) Na (2.8.1)

K(2.8.8.1)

Physical Property

1) Soft Metal

2) Shiny and

Silvery surface

that rapidly

tarnished in air

3) Low melting

and boiling points4) Low density

Chemical Properties1) All alkali

metals react with cold water

to form hydrogen

and an alkali

2) All alkali metals

burn with increasing

vigour from Li

down the group to

form white oxides

Group TrendsOn going

down, these

groups these

increases:

1) Density2)

Reactivity increases

Melting point and

boiling point

decreases

Group I

Group VII Elements – Halogens

The elements in Group VII of the periodic table are called halogens.

They form a group of reactive non-metals.


Halogens

Electronic Structure

1) Seven Electron on the

outer most shell

2) F (2.7) Cl

(2.8.7)

Physical Property

1) Non-Metal

2) At room temperatur

e, F and Cl exist as

gas, Br exists as liquid and I exists as

solid. 3) Low melting

point and boiling point

Chemical Properties

1) All halogens react with iron and

with other metals to form salts

called halides.

2) A more reactive halogen

will displace a

less reactive halogen from its halide

solution.

Group TrendsOn going

down, these

groups: 1) colour becomes

darker2)

Reactivity decreases3) Melting point and

boiling point

increases

Group VII

Group 0 Elements – Noble Gases

1. The elements in Group 0 or Group VIII are called noble gases or inert gases.

2. They are the least reactive elements in the Periodic Table.

3. Apart from helium which has 2 valence electrons, the other noble gases have 8 valence electrons.

4. Their full electronic structures make them unreactive.


Group 0 Elements – Noble Gases

Most of the noble gases can be obtained commercially through

fractional distillation of liquefied air.

Properties of the Noble Gases:

1) Monatomic elements (single atom)

2) Colourless gas at room temperature

3) Low melting point and boiling point that increase on going down

the group

4) Insoluble in water

5) Unreactive – They do not react to form compounds.



(c) Patterns in the Periodic Table

One useful way of classifying elements is as metals and non-metals.


(c) Patterns in the Periodic Table

Unfortunately, it is not easy to classify some elements in this way.

Take, for example, graphite and silicon.

These two elements have high melting points and high boiling points (like metals) but they have low densities (like non-metals).


The graphite nose cone of a space shuttle being tested in a furnace. Why is graphite used for the nose cone?

The nose cone is required to withstand the high temperature encountered during atmospheric entry and maintain the structure of the spacecraft,

Pg 15: They conduct electricity better than non-metals but not as well as metals. Elements with some properties like metals and other properties like non-metals are called metalloids. Because of this difficulty in classifying elements neatly as metals and non-metals, chemists looked for patterns in the properties and reactions of smaller groups of elements.


(d) Charges on ions

Charges on the ions formed are related to the group number and number of valence electrons.

Elements on the left side of the Periodic Table lose their valence electrons to form cations with charges corresponding to their group number.

Elements on the right side of the Periodic Table gain electrons to form anions. The charges on the anions corresponding to the number of electrons gained to fill their valence shells with eight electrons.

Element Na Mg Al Si P S Cl ArGroup number I II III IV V VI VII 0Formula of ion Na+ Mg2+ Al3+ - P3- S2- Cl- -

1.2 Formation of Ions 1.3 Periodic Table. Recall from Previous Lesson.

Documents

Transcript of 1.2 Formation of Ions 1.3 Periodic Table. Recall from Previous Lesson.