Atomic structure and the periodic table Flashcards
What is an atom?
An atom is the smallest part of an element that can exist.
What is an element?
An element is a substance of only one type of atom.
How are the elements listed and approximately how many are there?
There are listed in the periodic table and there are approximately 100.
Elements can be classified into 2 group bases on their properties, what are they?
Metals and non-metals.
Elements may combines through chemical reactions to form new products; what are they new substances called?
Compounds.
What is a compound?
2 or more elements combined chemically in fixed proportions which can be represented by formula.
Do compounds have the same properties as their constituent elements?
No, they have different properties.
What is a mixture? Does it have the same chemical properties as its constituent materials?
A mixture of 2 more more elements or compounds not chemically combined together; it does have the same chemical properties.
What the methods through which mixtures can be separated (there are five)? Do these involve chemical reactions?
- Filtration.
- Crystallisation.
- Simple distillation.
- Fractional distillation.
- Chromatography.
They do not involve chemical reactions.
Describe and explain simple distillation
Simple distillation is used to separate liquid from a solution - the liquid boils off an condenses in the condenser. The thermometer will read the boiling point of the pure liquid. Contrary to evaporation, we get to keep the liquid.
Describe and explain crystallisation/evaporation
Evaporation is a technique for a separation of a solid dissolved in a solvent from a solution such as salt from H₂O. The solution is heated until all the solvent evaporates; the solid stays in the vessel.
Crystallisation is similar, but we only remove some of the solvent by evaporation to form a saturated solution (the one where no more solid can be dissolved). Then, we cool down the solution. As we do it, the solid starts to crystallise, as it becomes less soluble at lower temperatures. The crystals can be collected and separated from the solvent via filtration.
Describe and explain fractional distillation
Fractional distillation is a technique for separation of a mixture of liquids. It works when liquids different boiling points.
The apparatus is similar to the one of simple distillation apparatus, with the additional fractional column placed on top of the heated flask.
The fractional column contains glass beads. It helps to separate compounds. In industry, mixtures are repeatedly condensed and vaporised. The column is hot at the bottom and cold at the top. The liquid will condense at different heights of the column.
Describe and explain filtration
Filtration is used to separate an insoluble solid suspended in a liquid. The insoluble solid (called a residue) gets caught in the filter paper, because the particles are too big to fit through the holes in the paper. The filtrate is the substance that comes through the filter paper.
Apparatus: filter paper + funnel.
Describe and explain chromatography
Chromatography is used to separate a mixture of substances dissolved in a solvent.
In paper chromatography, we place a piece of paper with a spot containing a mixture in a beaker with some solvent. The bottom of the paper has to be in contact with the solvent. The solvent level will slowly start to rise, thus separating the spot (mixture) into few spots (components).
What is a separating funnel?
A separating funnel is an apparatus for separating immiscible liquids. Two immiscible liquids of different densities will form 2 distinct layers in the separatory funnel.
We can run off the bottom layer (the liquid with greater density) to a separate vessel.
Describe the plum-pudding model
The atom is a ball of positive charge with negative electrons embedded in it.
Describe the Bohr model and how it came about
The nuclear model suggests that electrons orbit the nucleus at specific distances (shells) - it came about from the alpha scattering experiments.
Later experiments led to the discovery of smaller, positive particles in the nucleus; what are these particles called?
Protons.
What did the work of James Chadwick provide evidence for?
The existence of neutrons.
Describe the structure of an atom
The atom has a small central nucleus (made up of protons and neutrons) around which, there are electrons.
State the relative masses and relative charges of the proton, neutron and electron
Proton: mass = 1, charge = +1
Neutron: mass = 1, charge = 0
Electron: mass = very small/0, charge = -1
Explain why atoms are electrically neutral
They have the same number of electrons and protons.
What is the radius of an atom?
0.1 nm.
What is the radius of a nucleus and what is it compared to that of the atom?
1 x 10⁻¹⁴.
1/10,000.
What name is given to the number of protons in the nucleus?
Atomic number.
Atoms of the same element have the same number of which particle in the nucleus?
Protons.
Where is the majority of mass of an atom?
The nucleus.
What is the mass number?
The total number of protons and neutrons.
How does one calculate the number of neutrons using mass number and atomic number?
Subtract the atomic number from the mass number.
What is an isotope? Do isotopes of a certain element have the same chemical properies?
Isotopes are atoms of the same element (same no. of protons) but they have a different number of neutrons.
They have the same chemical properties as they have the same electronic structure.
What is the relative atomic mass?
The average mass value which takes the mass and abundance of isotopes of an element into account, on a scale where the mass of ¹²C is 12.
Give the electronic configurations of He (2), Be (4), F (9), Na (11), and Ca (20) to demonstrate how shells are occupied by electrons
He - 2 Be - 2.2 F - 2.7 Na - 2.8.1 Ca - 2.8.8.2
What are ions?
Ions are charged particles. They are formed when atoms lose electrons (positive ions) or gain (negative ions) electrons.
e.g. sodium is a positive ion Na⁺, has an electronic configuration of 2.8. This shows an atom of sodium has lost an electron.
Compare the properties of metals and non-metals
Metals:
- High boiling point.
- Can conduct heat and electricity.
- Shiny.
- Malleable.
- High density.
- Basic (oxides).
Non-metals:
- Low boiling point.
- Doesn’t conduct heat or electricity (exception is graphite as it can conduct electricity).
- Dull.
- Brittle.
- Low density.
- Acidic (oxides)
What is formed when a metal reacts with a non-metal?
An ionic compound (made of positive and negative ions).
What is formed when a non-metal reacts with a non-metal?
A molecular compound containing covalently bonded atoms.
Atoms share electrons from outer shell, as opposed to transferring electrons between each other like in ionic compounds.
Explain the following: solute, solvent, solution, miscible, immiscible, soluble, and insoluble
A solute is a substance that is dissolved in a solvent. Together, they form a solution.
Miscible refers to substances (mainly liquids) that mix together such as water and alcohol. Water and oil are immiscible as they do not mix.
Soluble refers to a substance that can be dissolved in a solvent such as salt in water. Insoluble substances won’t dissolve in a particular solvent.
What are the columns of the periodic table called?
Groups.
What are the rows of the periodic table called?
Periods.
Are elements in the same group similar or different?
They may have similar properties, as they have the same number of outer shell electrons.
In terms of energy levels, what are similarities between elements of the same period?
They have the same number of energy levels.
Elements occupy particular energy levels, with each electron in an atom at a particular energy level; which available energy level do electrons occupy?
The lowest available energy level.
What are elements of group 0 commonly known as?
Noble gases.
What makes the periodic table periodic?
Similar properties of elements occur at regular intervals.
Elements in the same group have the same number of electrons in their outer shell; what does this tell us about their chemical properties?
They have similar chemical properties.
In terms of shells, what is similar between elements in the same period?
Same number of shells.
What changes in shell number as one moves down a group?
The number of shells increases.
Early periodic tables were incomplete and elements were placed in inappropriate groups if what was to be followed?
The strict order of atomic mass.
Knowledge of what made it possible why the order based on atomic weights was not always correct?
Isotopes.
Mendeleev overcame some problems with the table by doing what? He also changed the order of some elements based on what?
He left gaps.
Changed order based on atomic weights.
The majority of elements are?
Metals.
Elements that react to form positive ions are?
Metals.
Elements that do not form positive ions are?
Non-metals.
Elements in group 1 are known as?
The alkali metals.
State characteristics of alkali metals
- All have one electron on their outer shell.
- Very reactive.
- Have low density.
- Stored under oil (prevent reactions with oxygen or water).
- Are soft (can be cut with knife).
- Low melting and boiling points.
How do group 1 elements react with non-metals? Why are these reactions similar for the different group 1 elements?
They form ionic compounds which are soluble white solids which form colourless solutions.
It is similar as they all have 1 electrons in their outer shell.
How do group 1 elements react with water?
They release hydrogen and form hydroxides which dissolve to form alkaline solutions. They react vigorously with water fizzing and the element moves around on the surface of the water.
How does the reactivity change moving down group 1? Why?
Reactivity increases as the atoms get larger and the distance between the nucleus and the outer electrons increases and thus attraction from the nucleus decreases, allowing them to more easily lose electrons.
State 5 characteristics of group 7
- 7 electrons in outer shell.
- Coloured vapours.
- Diatomic molecules.
- Form ionic salts/compounds with metals.
- Form molecular compounds with non-metals.
State group 7 elements and their states of matter
- Fluorine, F, F₂ is a pale yellow gas.
- Chlorine, Cl, Cl₂ is a pale green-yellow gas.
- Bromine, Br, Br₂ is a red-brown liquid.
- Iodine, I, I₂ is a greyish-black solid.
State three changes that occur in group 7 as one moves down the group
- Higher relative molecular mass (bigger)
- Higher melting and boiling point.
- Less reactive - less easily gain electrons.
A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; write the equations and state the colour change seen when chlorine/bromine reacts with sodium iodide
Cl₂ + 2NaBr → Br₂ + 2NaCl
Cl₂ + 2Br⁻ → Br₂ + 2Cl⁻
In this reaction, an orange colour of Br₂ would appear.
Cl₂ + 2NaI → I₂ + 2NaCl Cl₂ + 2I⁻ → I₂ + 2Cl⁻ Br₂ + 2NaI → I₂ + 2NaI Br₂ + 2I⁻ → Br₂ + 2Br⁻ In these 2 reactions, a brown colour of I₂ would appear.
A more reactive halogen displaces a less reactive one from an aqueous solution of its salt; explain the trend in reactivity of halogen in these reactions
Reactivity decreases down the group. As we go down the group, the atoms get larger, so an incoming electron will be less tightly held by the attractive forced from the nucleus. That’s why Cl₂ displaces B⁻ and I⁻.
Compare group 1 metals with transition metals
Group 1 metals and transition metals are heat and electricity conductors. They are shiny when polished and form ionic compounds with non-metals.
Transition metals have higher densities, harder and higher melting points than group 1 metals. They are less reactive than group 1 metals.
State 3 common characteristics of transition metals
- Ions with different charges.
- Coloured compounds.
- Catalytic properties.
What is a catalyst?
A catalyst is a chemical substance that increases the rate of a chemical reaction.
It is not used up over the course of the reaction.
State the colours of flames observed when lithium, sodium, as potassium burn in oxygen
Lithium - crimson red.
Sodium - yellow-orange.
Potassium - lilac.
Describe the properties of noble gases. Discuss the trend in boiling point down the group
- Non-metals.
- Gases.
- Monatomic.
- Low boiling points.
- Unreactive/inert (full outer shell; they don’t easily accept or lose electrons).
The boiling point increases down the group, as the atoms get larger (higher relative atomic mass)
