Particles and the Periodic table

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Dalton’s

particle model

* Scientific method

Developed a hypothesis

Made predictions based on the hipothesis

Carried out experiments to test the predictions

Formed a theory (model) using only the hypothesis that were supported by evidence

* Dalton's theory stated

All matter is

made up of tiny particles called atoms

Atoms are indestructible, and cannot be

created or destroyed.

The atoms in an element are all identical, and each element has its own type of atoms.

Symbols: he used symbols to represent the different atoms= elements (his symbols are not used today)

The difference in the atoms give each element its own physical properties that describe a substance on its own:

- colour - melting point - boiling point - densitiy

- strength - flexibility - conduction of heat - conduction of electricity

Physical changes:

- Only involve one substance

- Easy to reverse: water --->ice

- No new substances are formed

In compounds, each atom of an element is

always joined to a fixed number of atoms of the other elements.

Chemical properties of a substance: describe how it reacts with other substances. For example:

-flammability - reaction with acids - heat of combustion - toxicity - chemical stability

During chemical reactions, atoms rearrange,

to make new substances. No atoms are lost or gained so the mass of the reactants

is equal to the mass of the products.

For example:

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Atoms

Smallest units of matter

Cannot be broken down further by chemical means. [Atomos=indivisible (greek)]

They are the simplest form of molecule.

Its components are:

º Protons:

In the center (nucleus) of the atom

Positive charge

º Neutrons:

In the center (nucleus) of the atom

Uncharged

º Electrons:

Orbiting the atom

Negative charge

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Element

A solid, liquid or gas made of only one type of atom

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Compounds

Contain different atoms chemically joined together.

Some examples are:

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Physical Change vs. Chemical Change

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Mendeleev's Table (=Periodic Table)

Elements are represented by symbols = a capital letter or a capital letter and a lower case letter

H O Li Ca

The

symbol is the same in every language, even if the name of the element changes.

e.g. Sn(NO3)2

English-

Tin (II) Nitrate

Spanish

– Nitrato de Estaño (II)

Latin: (Sn): stannum (N): nitrum (O): oxys

Small number = atomic number (number of atoms in the molecule)

Large number = relative atomic mass (a measure of the mass of one atom of the element)

Groups = columns = show elements with similar properties:

IA = alkali metals// VIIA = halogens // VIIIA = noble gases

Periods = lines = group of elements ordered

in increasing

atomic

number

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Compounds vs. Mixtures

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FORMULAS

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Naming Compounds

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PHYSICAL TRENDS

Melting point = the temperature where a solid changes into a liquid

Boiling point = the temperature where a liquid starts to evaporate (changes into a gas)

Freezing point = the temperature where a liquid changes into a solid

Melting point: Trends Down the Groups

Main Group Metals- Melting point generally decreases as it goes down the group.

Non-metals- Melting point generally increases as it goes down the group.

Transition Metals- Melting point generally increases as it goes down the group.

Metalloids- melting point generally decreases as it goes down diagonally (along the "staircase")

Melting Point: Trends Across the Period

Excluding metalloids, melting point generally increases until group 6 and then decreases as you continue across the period.

Boiling Point: Trends Down the Groups

Main Group Metals- Boiling point generally decreases as it goes down the group.

Non-metals- Boiling point generally increases as it goes down the group.

Transition Metals- Boiling point generally increases as it goes down the group.

Metalloids- Boiling point generally decreases as it goes down diagonally (along the "staircase")

Boiling Point: Trends Across the Period

Excluding metalloids, the boiling point generally increases until group 5 (middle of transition metals) and then decreases as you continue across the period.

Density: Trends Down the Groups

Densities of elements increase down a group as atomic number increases

Density: Trends Across the Periods Across periods (left → right), densities increase, then decrease

o Elements with the greatest densities are at the center of period 6.

Metallic or Non-Metallic Properties

The "most metallic metal” is Francium (bottom left hand corner of the Periodic Table).

Helium is known as the “most non-metallic” element.

Remember = to be able to compare several elements at a time you have to see which is closer to either Fr or He, and decide which is the most metallic, or most non-metallic.

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Metals vs. Non-metals

Most elements are metals, rather than non-metals. The table summarises some differences in their properties.

Telling them apart

Notice that metals and non-metals have opposite properties to each other. It is usually easy to tell metals and non-metals apart, but some tests are more reliable than others.

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Specific Element Groups

Group 1 – the alkali metals

The Group 1 elements are called the alkali metals. They are placed in the vertical column on the left-hand side of the periodic table.

All the Group 1 elements:

are very reactive. They must be stored under oil to keep air and water away from them.

form alkaline solutions when they react with water, which is why they are called alkali metals.

Reactions with water All the alkali metals react vigorously with cold water. In each reaction, hydrogen gas is given off and the metal hydroxide is produced. The speed and violence of the reaction increases as you go down the group. This shows that the reactivity of the alkali metals increases as you go down Group 1.

Strong alkalis

The hydroxides formed in all of these reactions dissolve in water to form alkaline solutions. These solutions turn universal indicatorpurple, showing they are strongly alkaline. Strong alkalis are corrosive. Care must be taken when they are used - goggles and gloves should be worn.

Group 7 – the halogens

The Group 7 elements are called the halogens. They are placed in the vertical column, second from the right, in the periodic table.

Chlorine, bromine and iodine are the three common Group 7 elements.

Group 7 elements form salts when they react with metals. The term ‘halogen’ means 'salt former'.

Properties and uses of the

halogens

This table summarises some of the properties and uses of three halogens:

Reactivity of the halogens

Halogens get less reactive down the group. This is the opposite trend to that seen in the alkali metals in Group 1

Fluorine is the most reactive element of all in Group 7.

Astatine is the least reactive element.

You can see the trend in reactivity if you react the halogens with iron wool.

Trends in Group 7 (Halogens)

Increase DOWN the group

o Atomic size o Melting points

o Boiling points.

o Darker

Increase UP the group

o Reactivity

Group 0 – the noble gases The noble gases have the following properties in common:

they are non-metals

they are very unreactive gases

they are colourless

they exist as single atoms (they are monatomic)

Uses of the noble gases

The uses of the noble gases are usually linked to their inertness, or to their tendency to give off light when an electric current is passed through them.