L3 - The Periodic Table of Elements Flashcards
When was Dobereiner’s Law of Triads formed?
1817
Describe Dobereiner’s Law of Triads.
Organised elements in groups of three based on physical and chemical properties - found that the atomic masses of the 3 elements formed a pattern.
When was Newlands’ Law of Octaves formed?
1864
Describe Newlands’ Law of Octaves.
Organised elements in increasing order of atomic mass, and noticed that every 8th element exhibited similar properties.
When was Mendeleev’s Periodic Table formed?
1869
Describe Mendeleev’s Periodic Table.
- Arranged elements known at that time in order of relative atomic mass
- Realised that physical and chemical properties of elements were related to their atomic mass in a ‘periodic’ way, and arranged them so that groups of elements with similar properties were in vertical columns in his table
- Left gaps in horizontal rows; assumed it meant that these elements had not yet been discovered
When was Seaborg’s Periodic Table formed?
1940
Describe Seaborg’s Periodic Table.
- Expanded beyond Mendeleev’s initial 63 elements
- Vertical columns = groups
- Horizontal rows = rows
How is the Periodic Table arranged?
- Elements are arranged in order of atomic number, from left to right
- Progression runs from metals to non-metals across each period
Which group are the noble gases found in?
Group 8
State the Periodic Law.
“Properties of elements are periodic functions of their atomic numbers.”
What happens when elements are arranged in order of increasing atomic number?
There is a periodic pattern in their physical and chemical properties.
What are ‘families’ of elements?
Elements that share certain characteristics, not only in terms of observable behaviour, but also atomic structure.
State the common classifications of elements on the Periodic Table.
- Alkali Metals
- Alkaline Earth Metals
- Transition Metals
- Lanthanides
- Actinides
- Noble Gases
- Non-Metals
- Metalloids
Describe Group 1: Alkali Metals.
- Silver coloured
- Soft metals
- Highly reactive
- Rarely found in elemental form in nature
Describe Group 2: Alkaline Earth Metals.
- Silver coloured
- Soft metals
- Reactivity similar to alkali metals
Describe Group 7 (17): Halogens.
- Highly reactive
- Toxic
- Gases
- Low boiling / melting materials
Describe Group 8 (18): Noble Gases.
- Chemically inert
- Non-metallic
- Gaseous at standard conditions
Describe Metalloids.
- 6 elements
- Properties of both metals and non-metals
Describe Transition Metals.
- High densities, melting and boiling points
- Form coloured compounds and complex ions
- Variable valencies
- Ions readily undergo oxidation / reduction
- Can use electrons from two outer orbitals for combination with other elements
What are the Lanthanides?
15 elements with atomic numbers 57 - 71
Describe the Lanthanides.
- Also known as rare Earth metals
- Shiny and silvery-white
- Stain easily when exposed to air
- High melting and boiling points
What are the Actinides?
15 elements with atomic numbers 89 - 103
Describe the Actinides.
- Radioactive
- Very dense metals
- Distinctive structures
- Numerous allotropes may be formed
- Combine directly with most non-metals
What are the Non-Metals?
Groups 14-16 of the periodic table
Describe the Non-Metals.
- Not able to conduct electricity or heat very well
- Very brittle
- Cannot be rolled into wires / pounded into sheets
- No metallic lustre and do not reflect light
Describe the properties of elements in line with the general characteristics of groups.
- All elements of a given group possess very similar physical and chemical properties
- Regular gradation in properties when moving from top to bottom in a group
- Patterns in properties can also be seen going across a period
Describe the size of atoms in line with the general characteristics of groups.
- Increases on descending a group
Describe the metallic character of elements in line with the general characteristics of groups.
- Increases when moving from top to bottom in a group
- Apparent in groups 12, 13 and 14
Describe the reactivity of elements in line with the general characteristics of groups.
- Metals become more reactive on descending a group
- Non-metals become less reactive
Describe the number of electron shells in line with the general characteristics of groups.
- Equal to the number of the period to which the element belongs
- Going down a group, the number of electron shells increases by one at each step
Describe the number of valence electrons in line with the general characteristics of groups.
- Number of electrons in the outer shell of an atom is unchanged on moving down a given group
Describe valency in line with the general characteristics of groups.
- Valencies of all the elements in a group are generally the same
How are valencies calculated?
- Groups 1 - 4: Valency = Group Number
- Groups 4 - 8: Valency = (8 - Group Number)
Define Valency.
The number of chemical bonds formed by an atom.
The valency of a monoatomic ion is equal to its ______.
Charge
Which elements have multiple valencies?
- Phosphorus (P): Valency = 3/5
- Nitrogen (N): Valency = 3/5
- Transition metals
- Heavier elements, such as Lead (Pb): Valency = 2/4
Define Empirical Formula.
Expresses elemental composition of a compound as a simple whole number ratio.
Define Molecular Formula.
The exact number of each type of atom present in one molecule of the compound.
