Y11 Chemistry Test 1 - Atomic Structure and Bonding

i love you buckminsterfullerene

John Dalton’s Theory of the Atom

• atoms are indivisible structures

• all atoms of a given element have the same properties

• compounds are combinations of multiple atoms from different elements

• a chemical reaction is a rearrangement of atoms

  • the arrangement of atoms determine physical properties

  • based on law of conservation of mass and constant composition

J. J Thomson’s Theory of the Atom

• constructed the cathode ray tube

  • glass tube, emptied of air, which contained two sheets of metal, one positively charged (cathode) and one negatively charged (anode)

• found that particles would flow from the negatively charged to the positively charged plate, making them negatively charged particles

  • also found that they moved very easily from magnetic fields, meaning that they were of very low mass

  • further discovered this occurred in all elements, meaning electrons were present in all elements

• called these particles electrons, theorised they were embedded within a large positive filling/sphere thing

E. Rutherford’s Theory of the Atom

• Conducted Gold Foil Experiment

  • Assumed that due to Plum Pudding Model, atoms were low density high volume structures, and thus alpha particles would just knock away the atoms

  • Shot alpha particles at a very thin piece of gold foil, discovered that most passed right through, and a small few were completely bounced back

  • theorised atoms have a dense positive centre surrounded by orbiting electrons

Bohr’s Theory of the Atom

• Explained atoms emitting specific wavelengths of light as atoms moving to a higher energy level

  • Theorised electrons would absorb the required amount of energy to move to that higher level

  • As electrons always absorbed specific amounts of energy, the paths must be very well defined

• Believed that the atom was made up of a positive core surrounded by fixed paths of electrons

Chadwick’s Theory of the Atom

• Explained the unaccounted for weight that wasn’t taking up by the protons or electrons

  • shot alpha particles at a sheet of beryllium, causing an unknown particle to be released, which was unaffected by magnetic fields or charged, making it neutrally charged

  • When this neutral particle was shot at paraffin wax, it knocked away protons, making it highly penetrating

• believed they were basically the same weight as protons, and named them neutrons

Structure of Atom

Made up of:

• Nucleus

  • Central part of atom that has very low volume, but is highly dense

  • Contains protone and neutrons, similar mass\

• Electron Cloud

  • Makes up the majority of the volume within the atom

  • Takes up very little of the mass

  • Contains electrons

Isotopes

Variations of atoms which have the same amount of protons, but differing amounts of neutrons. Share the same chemical properties with other atoms of the same element, but different physical.

Each variation takes up the same proportion of the element throughout all substances

amu

atomic mass unit, equal to 1/12th of a carbon-12 atom, and is the unit for Relative Atomic Mass

Mass Spectrometer

A device used to measure the distribution of isotopes within a sample, in order to find the RAM of an element, and is made up of four parts, the ioniser, accelerator, deflector and detector

Ioniser

First part of the mass spectrometer that a sample goes through. Ionises a vapourised sample, converting them into cations (usually +1 charge)

Accelerator

The second part of the mass spectrometer that a sample goes through. Uses a negative and positively charged plate in order to accelerate and attract the cations toward the negative plates. Ions move through a small slit in the cathode, forming a single stream of positively charged particles

Deflector

Third part of MS that particles move through. Uses magnetic fields of varying intensities to move the streams toward the detector. As lighter isotopes are affected more by the magnetic field, thereby splitting the positive stream into multiple

Detector

Final part of the MS that a sample goes through. Measures the amount of collisions that occur on it for each stream of a certain weight of isotopes.

RAM Calculation Formula

(each isotope mass times their abundance) ÷ (the sum of all of the abundances)

Order of Electron Config

use data sheet

s (1 per energy level), p (3), d (5), f (7)

1s2, 2s2 2p6, 3s2, 3p6, 4s2, 3d10 so on so on

Ground State

The state of electrons that uses as little energy as possible by going to the closest possible position to the nucleus as possible

Excited State

The state of electrons where they absorb energy (heat, light, or electrical), causing them to move to a higher energy level (this is unstable). Upon return to ground state, a specific wavelength of light is released corresponding to the energy absorbed

Flame Tests

Tests in which metals are put into a flame in order to identify the metal based on the colour of the flame. When the metals is put in the fire, the electrons of the metal absorb the heat energy, causing them to move to a higher energy level. Once the electrons return to ground state, they will release a specific wavelength of light corresponding to the energy absorbed into the fire, causing the flame to change colour

Atomic Emission Spectroscopy

Process used to create the Atomic Emission Spectrum of an element. Excites the electrons of a substance by giving them sufficient energy to increase in energy level. Once they return to ground state, that element will release specific wavelengths corresponding to the energy absorbed, which are unique to that element. A prism can be used to separate all of the wavelengths, and then be recorded. This can be used to identify an element as each element has a unique AES

Atomic Absorption Spectroscopy

A device used in order to identify the concentration of a substance. Shoots the specific wavelength of light that excites a certain element, allowing them to identify if the element is present, and how much is present based on how much is absorbed. When an element absorbs light, it releases it in all directions, causing it to be weaker in one direction. Is made up of several parts, including a hollow cathode lamp, nebuliser/vapouriser, monochromator, and detector.

Hollow Cathode Lamp

Lamp that shoots the specific wavelength of light required to excite the element being identified. Is often coated with that element.

Nebuliser/Vapouriser

Part of AAS which converts the sample into a gas, allowing the wavelengths to pass through the vapour and be absorbed by electrons if the element is present

Monochromator

Part of AAS which is used to filter light. Removes all light going towards detector of a different wavelength than the specific one being studied

Detector

Final parts of the AAS. Measures the amount of the specific wavelength received compared to the amount emitted by the hollow cathode lamp. If:

• all of the light passes through, the substance is not present

• If only some of the light passes through, the substance is present (because the substance would emit it in all directions, causing less to go in one specific direction)

Absorbance

The measure of how much light is absorbed, and is used in AAS. The higher this is, the less light gets through

Calibration Curve

The line used to find the concentration from the absorbance given in the AAS. Is made by putting 5 or more known samples into the AAS, and using the absorbance found to plot them on a graph, and then create the line of best fit. From there, you can use the other absorbance levels to find where concentration they correspond to on the line of best fit

Core Charge

The net positive charge experienced by the valence electrons. Is found by subtracting the total number of protons from the number of non-valence electrons. Increases as you go right on the periodic table

Number of Energy Levels

The number of energy levels within an atom, creating distance between the valence electrons and the nucleus. Increases as you go down the periodic table

Electronegativity

The tendency of an atom to attract the electrons from other atoms. Increases with core charge as higher positive attraction means a stronger pull on the negatively charged electrons. Decreases with energy levels as distance from the nucleus weakens the pull from the protons

Atomic radius

The radius of an atom, or the distance between the centre and the outermost electrons. Decreases with core charge as higher attraction means greater pull on electrons, attracting them closer. Increases with energy levels as distance from nucleus means a weaker pull, meaning electrons are not pulled as closely to the nucleus

First Ionisation Energy

The amount of energy required to remove the first electron from an atom. Increases with core charge due to higher positive attraction meaning a greater pull on electrons and thus require more energy to remove. Decreases with energy levels as more distance from the nucleus causes a weaker pull on electrons, requiring less energy to remove

Metallic Properties

How metallic a substance is. Decreases with core charge due to metals generally having a low amount of valence electrons. Increases with energy levels

Successive Ionisation Energy

The amount of energy required to remove each successive electron from an element. Proved the existence of energy levels as the amount of energy required did not follow a linear fashion. Instead, would have sections of moving linearly broken up by large jumps. These jumps indicate a sudden increase in proximity to the nucleus, proving that electrons are found in groups, where groups are in varying distances from the nucleus

How Atoms Become Most Stable

When they achieve a full p orbital in their valence shell, causing them to be unreactive. Atomic properties will affect how this is achieved

The 4 Properties that indicate atomic arrangement

1. Malleability

2. Conductivity in Solid Form

3. Conductivity in Molten/Aqueous Form

4. Melting/Boiling point

Malleability

The ability of a substance to change shape, permanently, without breaking the bonds between particles. Relies on particles having non-directional bonding between them, meaning bonds can exist in all directions

Electrical Conductivity when Solid and Molten/Aqueous

The ability of a substance to carry and transport charges throughout it, which relies on the presence of mobile charged particles. This property can sometimes only be present in certain states, though this is not always the case

Melting/Boiling Point

The amount of thermal energy required for a substance to change states, which depends on the strength of the bonds between particles. The stronger the bonds are between particles, the more energy is required to overcome them

Metallic Bonding

The bonding that occurs between metals. Occurs when many atoms of a metal are together, and release their electrons past their p orbital, allowing them to move freely between the metallic ions. Forms a lattice structure of metallic ions all attracted by a sea of delocalised valence electrons

Properties of Metallic Bonds

• Are electrically conductive when both solid and molten/aqueous due to the sea of delocalised electrons (and metal ions when liquid) being able to act as mobile charged carriers

• Are malleable due to the electrons that attract metal ions being freely moving, meaning that when metal ions move, the electrons can still attract them

• Have high melting/boiling points due to the high electrostatic attraction between the sea of delocalised valence electrons and positive metal ions which requires a large amount of energy to overcome

Ionic Bonding

Bonding between (generally) a metal and non metal, where highly electronegative non-metals attract the low ionisation energy metals, allowing each element to achieve a full p orbital in their outermost energy level. Creates a lattice of alternating positive and negatively charged ions, with a strong electrostatic attraction between particles

Ionic Bonding properties

• Brittle, due to force applied causing like charged particles to align, and repel each other, breaking apart the substance

• Not electrically conductive when solid, as despite all particles being charged, there are no mobile particles as they are all kept in place by strong electrostatic bonds

• Electrically conductive when molten/aqueous as both the positive and negative ions become mobile, allowing them to transport charged

• Very high melting and boiling point due to an incredibly strong electrostatic attraction between the anions and cations, requiring much energy to overcome

Ion Formation

The process in which atoms give and take electrons so that each can achieve full p orbitals in their outermost energy level. The amount given and taken must be equal, allowing you to find the ratio of atoms

Ionic Formula

The formula used to work out the ratio of cations to anions.

Steps include

• Find the magnitude of the charges of each atom when ionised

• Find the lowest common multiple

• LCM/charge = number of atom

process is the same with polyatomic ions, just treating a polyatomic as one body

Electron Dot Diagrams for Ionic Substances

Used to show the amount of electrons in the highest energy level. You create by:

• Writing out each ion symbol

• Drawing the amount of electrons in the outermost energy level around it, differentiating between the regular electrons and those taken from the metal

• surround in square brackets, and place charge in top right corner

• Give a coefficient if more than 1 of that ion within the bond

Ionic naming scheme

Use the ion naming sheet, put cation first, then anion second

Covalent Molecular Bonds

Bonds where two or more non metals share electrons in order to achieve full p orbitals. Each group of atoms connected by bonds is known as a molecule. Each molecule has very strong intramolecular forces between covalently bonded atoms, but very weak Van der Waals charge [non-directional] between each molecule (intermolecular forces). As well as this, each molecule is neutrally charged

Covalent Molecular Properties

• Malleable due to the weak Van der Waals forces being non-directional, allowing molecules to move around each other

• An insulator when solid and liquid due to the molecules, despite being mobiles, being neutrally charged

• Low melting and boiling points due to the weak Van der Waals charges between molecules requiring little energy to overcome

Covalent Molecular Naming Scheme

Elements toward the top and left of the periodic table are generally put first in the name. The first element in the name does not include a number prefix unless there is more than one of it. The second element ends with ide usually, and includes a prefix indicating amount, even if there is just one

e.g., PCl₃ → Phosphorous Trichloride

Covalent Electrons Dot Diagrams

Are made with the following steps:

1. Find the total number of electrons an element has in it’s outermost energy level

2. Find the total number of electrons needed to achieve a full p orbital

3. Draw out atoms with dots that correspond for each electron needed, and connect each dot to each other to form one structure

4. Retract lines between dots so that each atom is next to each other

5. Convert each line into a pair of electrons

6. Draw all of the non-bonding valence electrons in as well

Coordinate Covalent Bonds

Bonds between atoms where the amount of electrons shared by each atom is not equal, commonly with one atom sharing none.

Non-Octet Rule Elements

Elements which in certain circumstances do not require 8 electrons to fill their outermost energy level.

e.g.,

• B = 6

• N = 7

• P = 10

• S = 12

Polyatomic Ions

Ions that contain multiple atoms. Occur in acids when they lose hydrogen atoms

Steps into finding electron dot diagram to polyatomic ions from acids

1. Add a hydrogen atom for each negative charge

2. Identify the central atom (not a H or O)

3. Connect a H_x^OO^{o (o and x representing electrons, not number)} to the central atom for every hydrogen

4. Check for the central bond’s config

   1. if stable, add any extra oxygens as coordinate covalent

   2. if not, add extra oxygens and introduce double bonds

5. Remove the hydrogens added at beginning to return to original form

6. Add square brackets and charge

Carbon monoxide Structure

CO

Ozone Structure

O₃

Hydronium

H₃O⁺

Ammonium

NH₄⁺

Covalent Network Substances

Substances made up of atoms that are covalently bonded together, not in groups, but in one large network of atoms intramolecularly bonded. Are generally made up of Group 14 Elements as they can make 4 covalent bonds

Covalent Network Properties

• Generally not malleable due to the intramolecular forces and network structure not allowing atoms to move very far before overcoming the covalent bond

• Generally high melting/boiling point due to the strong covalent bonds between atoms requiring a lot of energy to overcome

• Generally not conductive as each atom would be immobile and thus unable to transport charges

Carbon Allotropes

The several different covalent network substances carbon can form, depending on the conditions carbon experiences. There are 4 of these:

• Diamond

• Graphiye

• Buckminsterfullerene

• Amorphous Carbons

Diamond

An allotrope of carbons, where each carbon is bonded to another carbon in a tetrahedral arrangement (like the vertexes of a pyramid), which is highly stable and makes diamonds very hard. Are brittle, non-conductive, and have high melting and boiling points

Graphite

An allotrope of carbon, where each carbon atom is bonded to 3 others in a hexagon shape, making up individual sheets (known as graphene). There are weak Van der Waals charged between each sheet, making this allotrope slippery as the sheets can easily move around independent of one another. Intramolecular forces within sheets are very strong, requiring a lot of energy to break the bonds between carbon atoms.

• conductive when solid due to 4th electron being freely moving between sheets of graphene

• high melting and boiling point due to strong bonds

• Brittle because of non-directional bonding

Buckminsterfullerenes ❤

An allotrope of carbon, made up of carbon atoms bonded to three other carbons, creating hollow spheres of varying sizes. Is very slippy due to weak Van der Waals charges between balls, allowing them to roll over one another, making this a dry lubricant.

• High melting/boiling point due to strong bond between each carbon requiring much energy to overcome

• Not malleable due to covalent bonds not being able to move too far without breaking

• Not conductive, despite the 4th electron being delocalised, as the electrons are localised within the structure, and thus are unable transfer charges between fullerenes

Amorphous carbon

An allotrope of carbon where the carbon atoms are randomly bonded to one another without a consistent structure (e.g., coal, soot). Lack of uniform structure results in being quite weak.

• Not conductive due to a lack a consistent delocalised valence elctrons

• Brittle due to the non-uniform structure and lack of non-directional bonding due to covalent bonds

• High melting and boiling point due to very strong intramolecular forces requiring much energy to overcome