1
Q
True or false: metal elements and non-metal elements have different characteristic physical properties?
A
True
2
Q
What is a physical property?
A
A characteristic that can be observed or measured
3
Q
Physical properties of metal elements:
A
- Appearance: shiny
- Melting and boiling point: usually high
- State at room temperature: solid
- Malleable or brittle when solid: malleable (they bend without shattering)
- Ductile or non-ductile when solid: ductile (they can be pulled into wires)
- Thermal and electrical conductivity: good conductors
4
Q
Physical properties of non-metal elements:
A
- Appearance: dull
- Melting and boiling point: usually low
- State at room temperature: about half are solid; about half are gas
- Malleable or brittle when solid: brittle (they shatter when hammered)
- Ductile or non-ductile when solid: non-ductile (they snap when pulled)
- Thermal and electrical conductivity: poor conductors (they are insulators)
5
Q
How is the Periodic Table arranged?
A
- The Periodic Table is a table in which all the elements are arranged in rows and columns, in order if increasing atomic number
- Metal elements are placed on the left-hand side of the Periodic Table, and non-metal elements are placed on the right-hand side
- They can be separated by a zigzag boundary
- Some of the elements on this boundary have properties of both metals and non-metals
6
Q
True or false: metal elements and non-metal elements have different characteristic chemical properties?
A
True
7
Q
What is a chemical property?
A
A characteristic of a substance that can only be determined by studying its chemical reactions
8
Q
How are metals and non-metals different in reactions?
A
- Metals lose electrons to form positive ions, but non-metals gain electrons to form negative ions
- Metal do not react with each other (they mix to form alloys), but non-metals react with each other to produce compounds that consist of molecules
9
Q
How are metal oxides and non-metals oxides different?
A
- Metals and non-metals may react with oxygen to produce oxides, but these have different properties
- If metal oxides dissolve in water they produce alkaline solutions
- If non-metal oxides dissolve in water they produce acidic solutions
10
Q
What is the special name for a horizontal row within the Periodic Table?
A
A period
11
Q
What is the special name for a vertical column within the Periodic Table?
A
A group
12
Q
How are elements arranged in the Periodic Table?
A
- The groups and periods are numbered to help identify them
- If you look from left to right across a period, you will see that the atomic number increases by 1 going from one element to the next
- This means that the number of electrons in each atom also increases by 1 each time
- The elements in a group have similar chemical properties
- This is due to the arrangement of their electrons
13
Q
How can you work out electronic structures?
A
You can work out electronic structures by counting from hydrogen, period by period, until you reach the element you want
14
Q
How is electronic structure related to the Periodic Table?
A
- There are links between the numbers in the electronic structure of an element and its position in the Periodic Table
- The last number equals the non-IUPAC group number
- However, atoms of Group 0 elements (IUPAC Group 18) all have full outer shells
- The number of numbers equals the period number
- The sum of the numbers equals the atomic number
15
Q
How are electrons arranged in atoms?
A
- The electronic structure of an element shows how the electrons are arranged in its atoms
- The outermost occupied shell in an atom is called the outer shell
- The electrons in atoms are arranged around the nucleus in shells
- Different shells can hold different numbers of electrons
16
Q
What are ions?
A
- An ion is an electrically charged particle formed when an atom, or group of atoms, loses or gains electrons
- Metal atoms lose electrons to form positive ions
- Non-metal atoms gain electrons to form negative ions
- The number of protons and neutrons do not change when an atom forms an ion
- Just like atoms, you cannot see individual ions
17
Q
What are the electronic structure of ions?
A
- You can work out ion’s electronic structure if you know the electronic structure of the original atom, and the number of electrons lose or gained
- For example, the electronic structure of a sodium atom is 2.8.1
- It loses its outer electron when it forms a sodium ion
- The full second shell is now the outer shell and the ion’s electronic structure is 2.8
- In a similar way, the electronic structure of a chloride ion is 2.8.8 because it forms when a chlorine atom (2.8.7) gains one electron and completes its outer shell
- Atoms and ions with full outer shells are stable
18
Q
What are electron diagrams?
A
- An electron diagram represents the electronic structure of an atom or ion
- You draw a circle to represent each shell, and dots or crosses to represent its electrons
- Ions go inside brackets with the charge written at the top right, and the element’s symbol may be written at the centre instead of showing a nucleus
- Note that electrons are all the same in these diagrams
- The use of dots or crosses lets you model which atom provided a particular direction
19
Q
How do ionic compounds form?
A
- When a metal reacts with a non-metal, electrons are transferred from the metal atoms to the non-metal atoms so both achieve more stable electronic structures
- The metal atoms become positive ions and the non-metal atoms become negative ions
- For example, when sodium reacts with chlorine, the outer electron of each sodium atoms transfers to the outer shell of a chlorine atom, forming Na+ ions and Cl- ions
- You can model the ions in the ionic compound that is formed using a dot-and-cross diagram
- You can show the electrons from one atom as dots, and the electrons from the other atom as crosses
20
Q
What is the structure and bonding in ionic compounds?
A
- Ionic compounds in their solid state contain positive and negative ions arranged in a regular way
- This arrangement is called a giant ionic lattice
- The ions are held in place by ionic bonds, which act in all directions
- Ionic bonds are strong electrostatic forces of attraction between oppositely charged ions
- Space-filling models are one way of representing ionic compounds
21
Q
What does ‘giant ionic lattice’ mean?
A
- The word ‘giant’ tells you that the arrangement is repeated many times, not that it is huge
- The word ‘ionic’ reminds you that the structure contains ions, and ‘lattice’ means that the arrangement is regular and not random
22
Q
Models of giant ionic lattices:
A
- A giant ionic lattice exists in three dimensions, but you can only draw it in two dimensions
- You could make a ball-and-stick model
- Each plastic ball represents an ion and each plastic link represents an ionic bond
- These models give you a clearer idea of the structure and shape of the lattice, but they do have limitations
- Remember that ions are close together, and that bonds are forces rather than physical objects made from matter
23
Q
What are covalent bonds?
A
- A covalent bond is a shared pair of electrons
- Covalent bonds form between two non-metal atoms when the atoms get close enough to share electrons in their outer shells
- By sharing electrons, the atoms complete their outer shells
24
Q
How can covalent bonds be modelled?
A
- Covalent bonds can be modelled using dot-and-cross diagrams
- The electrons from one of the bonded atoms are shown as crosses
- Each pair of electrons in the shared area between the overlapping circles represents a covalent bond
- Only the outer shells are usually shown
25
What are simple molecules?
- Hydrogen, oxygen, water and carbon dioxide all exist as simple molecules
- A molecule is a particle in which non-metal atoms are joined to each other by covalent bonds
- A simple molecule is a molecule that only contains a few atoms
- These substances can be modelled using dot-and-cross diagrams
26
What is the structure and bonding in simple molecules like?
- Covalent bonds involve electrostatic forces of attraction, just like ionic bonds do
- However, for a covalent bond, the forces are between the nucleus of each bonded atom and the shared electrons
- The covalent bonds between atoms in a simple molecule are strong, but the intermolecular forces between the molecules are weak
27
Ball-and-stick model for simple molecules:
- You can make ball-and-stick models for simple molecules, just as you can for ionic compounds
- This model has limitations: both the sizes of the atoms and the length of the bonds are exaggerated, and it suggests that the electrons that make the bonds do not move
28
Displayed formula model for simple molecules?
- You can also draw a displayed formula for simple molecules
- In these formulae, each atoms is represented by its chemical symbol, and each covalent bond by a straight line
- Notice that simple molecules have shapes
- However, this model is limited as it does not show the three-dimensional shape of the molecule
29
What are giant covalent structures?
- A giant covalent structure consists of very many non-metal atoms joined by covalent bonds and arranged in a repeating regular pattern called a giant lattice
- These structures are also called giant covalent lattices
- Diamond is a form of carbon
- It exists as a giant covalent structure in which each carbon atom is joined to four other carbon atoms by covalent bonds
30
What are the chemical formulae of giant molecules?
- Just like in ionic compounds, where very many ions are involved, giant covalent structures have very many atoms
- It would make little sense for you to try to write a chemical formula with these huge numbers in it
- Instead, you use the empirical formula for the substance
- You will remember that this formula shows the simplest whole number ratio of atoms of each element
- This is why the formula for diamond is given in chemical equations as C
31
Empirical formula of a giant covalent structure of silica:
- Each silicon atom is covalently bonded to four oxygen atoms
- However, each oxygen atom is also bonded to two silicon atoms
- Taken over the whole structure each silicon atom is, on average, bonded to two oxygen atoms
32
What are polymers?
- All polymers, whether they are artificial or natural, are made from many smaller molecules called monomers
- These monomers are able to join end to end in chemical reactions, producing longer polymer molecules
- For example, many ethene molecules can join end to end to make poly(ethene), often called polythene
- Another example, many amino acid molecules can join end to end to make a protein, such as keratin in hair
33
How are polymer molecules modelled?
- Monomers are simple molecules
- The consist of a few non-metal atoms joined to each other by covalent bonds
- You can usually model monomers using dot-and-cross diagrams, space-filling models, and ball-and-stick models
- This is much more difficult for polymer molecules
34
A simple model for two different types of polymer:
- Each polymer molecule is drawn as a wavy line
- These sometimes have straight lines between them to represent covalent bonds between individual polymer molecules
- There are weak intermolecular forces between polymer molecules but these are not shown
- The polymer chains in this tangled web are relatively easy to separate
- Chains joined together by strong covalent bonds is called cross linking
- *(check Kerboodle for diagram)
35
What are polymers made of?
- Some polymers are made from several different types of monomer, for example proteins and DNA
- However, other polymers are made from one type of monomer, for example poly(ethene) is only made from ethene
- Poly(ethene) can be modelled using the idea of a repeating unit
- This is a section of the polymer molecule that is repeated over and over again, rather like links on a chain
36
What is the structure of metals like?
- All metals, apart from mercury, are in the solid state at room temperature
- Their atoms are packed together in a regular way, forming a giant metallic lattice
- This is modelled by drawing circles or spheres arranged in a regular pattern, touching each other
37
What are metallic bonds like?
- In reactions with non-metals, metal atoms lose electrons from their outer shell to form positively charged ions
- This also happens in metals themselves
- Electrons leave the outer shells of the metal atoms, forming a 'sea' of electrons around positively charged metal ions
- These electrons are free to move through the structure of the metal, so they are called delocalised electrons
- Metallic bonds are the strong electrostatic forces of attraction between the delocalised electrons and the closely packed, positively charged metal ions
- *(check Kerboodle for diagram)
38
Localised and delocalised:
- Something that is 'localised' is restricted to a particular place
- Something that is 'delocalised' is free to move from its usual place
- For example, when you sit in your usual place in the laboratory you are localised, but you become delocalised when you move around the laboratory during a practical activity
39
What is a disadvantage of 2D models of metals?
- A metallic structure extends in three dimensions
- You lose some information when you represent the structure and bonding in metals in two dimensions
- *(check Kerboodle to compare diagrams)
40
What did Mendeleev do for the Periodic Table?
- Mendeleev's arrangement was not the first attempt by chemists to organise the elements into a table
- However, it was the most successful and it led to our modern Periodic Table
- Mendeleev had been considering his own and other scientists' evidence about the elements for several years before his first table
- Mendeleev arranged all the elements known at the time in order of increasing atomic weight, and he grouped together the ones with similar chemical properties
- However, he swapped the positions of tellurium and iodine because he felt that this matched their chemical properties better
- Mendeleev left spaces for elements he thought would exist but were not yet discovered, and predicted their properties from those nearby elements
- Mendeleev's first Periodic Table showed groups as rows, not columns
- By 1871 he had rotated his table so that groups were in columns, as in the modern Periodic Table
- Three of his predicted elements were discovered between 1875 and 1886
- They were found to have similar properties to the ones he had predicted years before
41
What prior information and evidence did Mendeleev use about elements to create his first table?
- The atomic weights of the known elements, similar to our modern relative atomic masses
- Knowledge of the chemical reactions of different elements
- Knowledge of physical properties, such as melting points and boiling points
42
Why is the modern table in order of atomic number?
- Mendeleev developed his table without knowing about atomic structure
- During Mendeleev's lifetime, the atomic number of an element was just its position in the Periodic Table
- Mendeleev died in 1907, before the proton was discovered
- It was not until 1913 that Henry Moseley, an English physicist, discovered that an atom's atomic number was actually the number of protons in its nucleus
- Moseley's work showed that there were seven gaps left to fill in the 1913 Periodic Table
- It also explained why Mendeleev had been right to swap tellurium and iodide around
43
A new group - what happened?
- Lord Rayleigh and William Ramsay discovered argon in 1894
- No-one had predicted its existence, not even Mendeleev
- Ramsay discovered helium the following year
- Both gases are inert
- Mendeleev thought that elements should be able to react with other elements, so he was reluctant to believe that helium and argon were elements
- The situation changed during 1898 when Ramsay discovered three more new elements
- Just like argon, Mendeleev had not predicted the existence of neon, krypton, or xenon
- All three are very unreactive gases
- Ramsay believed that the five gases he had discovered formed a new group of elements
- He suggested to Mendeleev that they should be placed next to Group 7 (IUPAC Group 17) in the Periodic Table
- Mendeleev accepted that the gases really were elements and that they should be placed there
44
Do the following groups become more or less reactive as you go down the group: Group 1, 2, and 7?
Elements in Groups 1 and 2 become more reactive as you go down the group, and Group 7 elements become less reactive
45
What tells us that there is a link between the position of an element in the Periodic Table and its chemical properties?
- Elements are arranged in order of increasing atomic number
- The atomic number is the number of protons in an atom
- The number of electrons in an atom is equal to the number of protons
- Electronic structure is determined by the number of electrons
- The electronic structure of an element determines its chemical properties
46
Group 1: Type of element, Reactivity, Electronic structures, Ions formed in reactions
- Type of element: metal
- Reactivity: very reactive
- Electronic structures: end in 1
- Ions formed in reactions: +1
47
Group 2: Type of element, Reactivity, Electronic structures, Ions formed in reactions
- Type of element: metal
- Reactivity: reactive
- Electronic structures: end in 2
- Ions formed in reactions: +2
48
Group 7: Type of element, Reactivity, Electronic structures, Ions formed in reactions
- Type of element: non-metal
- Reactivity: very reactive
- Electronic structures: end in 7
- Ions formed in reactions: -1
49
Group 0: Type of element, Reactivity, Electronic structures, Ions formed in reactions
- Type of element: non-metal
- Reactivity: very unreactive
- Electronic structures: outer shells are full
- Ions formed in reactions: do not react
Chemistry
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