Atomic structure and the periodic table 2 Flashcards
The periodic table
How were elements classified in the early 1800s?
By atomic weight.
What had not been discovered in the early 1800s?
Protons
Neutrons
Electrons
Describe two changes that Mendeleev made to early periodic tables.
He left gaps in order to keep elements with similar properties in the same group.
He switched the order of elements based on their properties, even if their atomic weights were no longer in order.
What are the problems with the early periodic tables?
They were incomplete.
Some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
What did some of the gaps left by Mendeleev indicate?
The existence of undiscovered elements.
Mendeleev could predict what their properties might be.
Elements with properties predicted by Mendeleev were…
…discovered and filled the gaps.
When they fit the patterns, this helped confirm Mendeleev’s ideas.
Knowledge of isotopes made it possible to do what?
Explain why the order of elements in early periodic tables, based on atomic weights, was not always correct.
Isotopes of the same element have different masses but the same chemical properties so occupy the same position in the periodic table.
What do we call atomic weight now?
Relative atomic mass
Where does the periodic table get its name?
Because similar properties of elements occur at regular intervals - ‘periodically’. This was noticed at early stages.
Date of Dmitri Mendeleev’s table of elements.
1869
How many elements were in Mendeleev’s original table of elements?
50
Give an example of Mendeleev changing the periodic table from order of atomic weight because of the properties of elements.
Te and I
Iodine has a smaller atomic weight (relative atomic mass) but is placed after tellurium as it has similar properties to the elements in group 7.
How are the elements of the periodic table arranged?
In order of increasing atomic (proton) number.
This means that elements with similar properties are in columns - known as groups.
What do elements in the same group in the periodic table have in common?
They have the same number of electrons in their outer shell (outer electrons).
This gives them similar chemical properties.
What are the vertical columns on the periodic table called?
Groups
How do we work out how many electrons are on the outer shell of atoms of an element?
The group number tells you this (1,2,3,4,5,6,7,) apart from group 0.
Elements in the same group are likely to react…
…in a similar way.
Using the fact that elements in the same group have similar properties, what can we do?
Predict the properties of unknown elements.
Make predictions about reactivity.
What are the rows called on the periodic table?
Periods.
What does the period of an element tell you?
How many electron shells there are (start at hydrogen as period 1!)
Chlorine reacts in a similar way to bromine. Suggest a reason why.
Both chlorine and bromine are in group 7 and so have the same number of electrons in their outer shell.
Metals
Elements that react to form positive ions.
Non-metals
Elements that do not form positive ions when they react.
Are most of the elements in the periodic table metals or non-metals?
Metals
Where are metals found in the periodic table?
To the left and towards the bottom.
Where are non-metals found in the periodic table?
Towards the right and top.
What do atoms generally react to do?
Gain a full outer shell and become stable. They do this by losing, sharing, or gaining electrons.
Why are metals to the left of the periodic table more reactive?
They don’t have many electrons to lose so not much energy is needed for the elements to react and form positive ions.
Why are metals towards the bottom of the periodic table more reactive?
Their outer electrons are far from the nucleus so the electrostatic forces of attraction are weaker.
So, not much energy is needed for the elements to react and form positive ions.
Why is forming positive ions difficult for non-metals?
They are either to the right of the periodic table where they have lots of electrons that would have to be lost to gain a full outer shell…
Or towards the top where the outer electrons are close to the nucleus so feel a strong attraction.
It would take a lot of energy to lose the electrons.
What is more feasible for non metals to do than lose electrons?
Either share or gain electrons to gain a full outer shell.
Why are the basic physical properties of all metals similar?
All metals have metallic bonding.
Basic physical properties of metals
-Strong
-Malleable
-Good conductors of heat and electricity
-High melting and boiling points
Malleable
Can be bent or hammered into different shapes.
Why don’t non-metals have the same properties as metals?
They don’t have metallic bonding.
Basic physical properties of non-metals
-Dull
-Brittle
-Lower density
-Poor conductors of electricity (generally)
-Aren’t always solids at room temperature
Non-metals form a variety of different structures, so…
…have a wide range of chemical properties.
Where are transition metals found in the periodic table?
In the centre.
Transition metals are _____ and have the _____________.
Typical metals
Properties you would expect of a ‘proper’ metal: dense, strong, and shiny.
What are the special properties of transition metals?
-They can have more than one ion
-They are often coloured, and so compounds that contain them are colourful
-They often make good catalysts
Example of transition metals with more than one ion
Copper forms Cu⁺ and Cu²⁺ ions.
Cobalt forms Co²⁺ and Co³⁺ ions.
What transition metal compound is yellow?
Potassium Chromate (VI)
Which transition metal compound is purple?
Potassium (VII) magnate
What is a nickel-based catalyst used in?
The hydrogenation of alkenes.
What is an iron catalyst used in?
The Haber process.
What are the elements in group 0 of the periodic table called?
The Noble Gases.
What are the noble gases?
Inert, colourless gases (at room temperature).
Give examples of group 0 elements.
Helium
Neon
Argon
Why are the noble gases unreactive?
Their atoms have stable arrangements of electrons (eight electrons in their outer shell, except for helium, which has only two electrons).
The noble gases do not easily form what?
Molecules.
Trends as you go down group 0
The boiling points of the noble gases increase going down the group (with increasing relative atomic mass).
Why does the boiling point of the noble gases increase as you go down the group?
The number of electrons in each atom increases as you go down the group.
This means that the intermolecular forces between each atom become greater, which take more energy to overcome.
How do we predict the boiling point of an element sandwiched between two other elements with known boiling points?
You can predict the boiling point will be halfway between the other two boiling points.
So, add them together and divide by 2.
Are the noble gases diatomic?
No. They exist as monatomic gases.
Monatomic (gases)
Single atoms not bonded to each other.
Why are the noble gasses non-flammable?
They are inert (so don’t react with much at all).
This is because they don’t need to lose or gain outer electrons to become stable.
What are the elements in group 1 of the periodic table called?
The alkali metals
Why do the alkali metals have characteristic properties?
Because of the single electron in their outer shell.
What are the (similar) properties of all alkali metals?
-Soft
-Low density
-Low melting and boiling points
The alkali metals are…
Very reactive!
Trends as you go down group 1
-Reactivity increases
-Lower melting and boiling points
-Higher relative atomic mass
Why does the reactivity of group 1 elements increase as you go down the periodic table?
The electron shells become further away from the nucleus.
This means that the electrostatic forces are weaker.
Which means the outer electron is more easily lost.
What type of compound do alkali metals form?
Ionic compounds with non-metals.
What is the charge on the ion of an alkali metal?
1+
What are ionic compounds?
(generally) white solids that dissolve in water to form colourless solutions.
How do group 1 (alkali metals) react when placed in water?
Vigorously.
As we go down group 1, the reactions become more violent because the metals are more reactive.
Alkali metal + Water → What products?
Metal hydroxide + Hydrogen
Symbol equation for reaction of sodium with water.
2Na (s) + 2H₂O (l) → 2NaOH (aq) +H₂ (g)
What are metal hydroxides?
Metal compounds that dissolve in water to produce alkaline solutions.
The amount of energy given out by the reaction of an alkali metal with water…
…increases down the group.
The reaction with potassium releases enough energy to ignite hydrogen.
How do group 1 (alkali metals) react when heated chlorine gas?
Vigorously.
Alkali metal + Chlorine → What product?
Metal chloride salts e.g. sodium chloride.
Symbol equation for the reaction of sodium heated in chlorine gas.
2Na (s) + Cl₂ (g) → 2NaCl (s)
Alkali metal + Oxygen → What product?
Metal oxide
(the type will differ depending on the Group 1 metal used).
What does Lithium react with oxygen to form?
Lithium oxide (Li₂O).
What does Sodium react with oxygen to form?
A mixture of sodium oxide (Na₂O) and sodium peroxide (Na₂O₂).
Sodium peroxide
Na₂O₂
What does Potassium react with oxygen to form?
A mixture of potassium peroxide (K₂O₂) and potassium superoxide (KO₂).
potassium peroxide
K₂O₂
potassium superoxide
KO₂
Are group 1 metals or transition metals more reactive?
Group 1 (alkali) metals.
They react more vigorously with water, oxygen, and group 7 elements, for example.
Group 1 vs Transition metals
-Group 1 (alkali) metals are less dense, strong, and hard than transition metals.
-Group 1 metals have much lower melting points than transition metals (manganese = 2000°C vs sodium =98°C).
What are the elements in group 7 of the periodic table called?
The halogens
Why do the halogens have similar reactions?
Because they all have 7 electrons in their outer shell.
Are the halogens diatomic?
Yes
Diatomic
Molecules made of pairs of atoms.
What are the 7 diatomic elements?
hydrogen, nitrogen, oxygen, fluorine, chlorine, iodine, bromine
Trends as you go down group 7
As you go down group 7, the halogens:
-become less reactive
-have higher melting and boiling points
-have higher relative atomic masses
What are the halogens?
Non-metals with coloured vapours.
Fluorine (F₂)
A very reactive, poisonous yellow gas.
Chlorine (Cl₂)
A fairly reactive, poisonous dense green gas
Bromine (Br₂)
A dense, poisonous, red-brown volatile liquid
Iodine (I₂)
A dark grey crystalline solid or a purple vapour.
A more reactive halogen can displace a less reactive halogen from what?
An aqueous solution of its salt (a bromide or iodide).
What type of compounds do the halogens form?
Covalent bonds with other non-metals, forming simple covalent structures.
Ionic bonds with metals, forming ionic structures.
What type of ions do halogens form?
1- ions called halides (F-, Cl-, Br-, and I-)
What do HCl, PCl₅, HF, and CCI₄ have in common?
They all contain covalent bonds and contain halides.
What colour are halide salts? (e.g. KCl, KBr, KI)
colourless
what colour is bromine water?
[ Br₂ (aq) ]
orange
what colour is chlorine water?
[ Cl₂ (aq) ]
colourless
what colour is iodine water?
[ I₂ (aq) ]
brown
More reactive halogens displace…
…less reactive ones. This can lead to a colour change.
How did Dalton describe atoms?
Small, solid, inelastic spheres that could not be divided.
How did JJ Thomson describe atoms?
A cloud of positive charge with tiny negative electrons randomly scattered within the cloud that could be knocked off
(plum pudding model).
How did Rutherford describe the atom?
-All the positive charge concentrated in a tiny nucleus
-Electrons randomly scattered
How does the nuclear model describe the atom?
-Protons and neutrons in the nucleus
-Electrons orbiting in shells
Why is it important that scientists check new findings?
To ensure they’re reproducible.
