Topic 1 - Atomic Structure and The Periodic Table Flashcards
What charge do atoms have?
Neutral charge - they have the same number of protons and electrons. The equal but opposite charges will then cancel each other out
What is the nucleus of an atom? What is its charge?
The nucleus is the central part of the atom. It contains the protons and the neutrons and has a positive charge due to the protons and the neutral electrons. Almost the whole mass of the atom is concentrated in the nucleus
What is the approximate radius of an atom?
Atoms have a radius of about 0.1 nano-metres
What are some features of electrons? Where are electrons found on the atom?
Electrons orbit the nucleus in ‘shells’. They have a negative charge and have virtually no mass
What can we deduce from the nuclear symbol of an atom? How can we use it to find the number of neutrons in the atom
From the nuclear symbol of an atom, we can deduce its atomic (proton) number and its mass number. We can then subtract the proton number from the mass number to determine the number of neutrons in the atom
What are isotopes?
Isotopes are different forms of the same element which have the same number of protons and electrons but a different number of neutrons. Isotopes will therefore have different mass numbers
What is a compound?
Compounds are substances formed of two or more elements. The atoms in chemical compounds are each in fixed proportions and are held together through chemical bonds
What do compounds formed from metals and non-metals consist of?
Compounds formed of metals and non-metals consist of ions. The metal ions lose electrons to form positive ions whilst the non metal gains electrons to form negative ions. These opposite charges mean that the ions are strongly attracted to each other through ionic bonding
What do compounds formed from non-metals consist of?
Compounds formed from non-metals consist of molecules. Each atom shares an electron with another atom in a process known as covalent bonding
What is a mixture?
A mixture contains two or more substances that are not chemically bonded together
How are mixtures unlike compounds?
- Substances in a mixture can be separated using physical methods such as filtration, freezing and distillation
- Mixtures have varying compositions whereas compounds have a fixed, definite formula
- In a mixture, substances keep their properties whilst this is not always the case in a compound
How do the properties of a mixture change relative to the properties of the individual substance?
Properties of a mixture are just mixtures of the properties of the individual parts. For example, a mixture of iron powder and sulphur powder will show the properties of both iron and sulphur. It will contain grey, magnetic pieces of iron and bright yellow pieces of sulphur
Name three techniques we can use to separate mixtures
Filtration, Crystallisation, Chromatography (Evaporation, Simple Distillation)
Describe the method to carry out Evaporation
- Pour the solution into an evaporating dish
- Slowly heat the solution (the solvent will evaporate and the solution will become concentrated - allowing for the formation of crystals)
- We then keep heating the dish until there is no solvent left and only crystals remain
Describe the method to carry out crystallisation
- Pour the solution into an evaporating dish and gently heat it. Some of the solvent will evaporate and the solution will become more concentrated
- Once some of the solvent has evaporated, remove the solution from the heat and allow it to cool
- The salt should then begin to form crystals as it becomes insoluble in the cold, highly concentrated solution
- We then filter the crystals out of the solution and leave them in a warm place to dry
Describe a method that could be used to separate rock salt
We could use a process of filtration and crystallisation to separate rock salt;
- Grind the mixture so that the salt crystals are small and will dissolve easily
- Put the mixture in the water and stir. The salt is soluble and therefore will dissolve whilst the sand is insoluble and does not dissolve
- Filter the mixture, the grains of sand wont fit through the pores of the filter paper therefore they will be collected whilst the salt passes through
- We then evaporate the water to obtain salt crystals in a dish
When could we use a process of filtration?
- Filtration could be used to separate an insoluble solid from a liquid reaction mixture
- We could also use filtration during a purification process as solid impurities could be filtered out through filtration
Through what process could we separate different dyes in an ink?
Paper chromatography
Why do we use a pencil to draw a line at the bottom of the chromatography paper?
We use a pencil line as if we were to use pen ink, it would be dissolve in the solvent. Pencil however is insoluble
What was John Dalton’s theory of the atom?
At the start of the 19th century, John Dalton described atoms as solid spheres and said that different spheres made up the different elements
What was JJ Thompson’s theory of the atom?
JJ Thompson was able to conclude from his experiments that an atom had to contain even smaller, negatively charged particles. The ‘plum pudding’ model of the atom was developed showing the atom as a ball of positive charge with electrons stuck in it
Through what experiment did Rutherford disprove the ‘plum pudding’ model of the atom?
Alpha particle scattering experiment
Describe how Rutherford carried out his experiment. What did they find?
- Positively charged alpha particles were fired at a thin sheet of gold
- They found that though most of the particles passed straight through the gold sheet, some were deflected more than expected and a small number even were deflected backwards
What did Rutherford’s experiment show?
From the experiment, Rutherford was able to display the nuclear model of the atom. In this, most of the mass is concentrated in the nucleus at the centre of the atom. A ‘cloud’ of negatively charged electrons then orbits this nucleus - therefore most of the atom is merely empty space. When alpha particles came near the positive charge of the nucleus, they were deflected. However, because most of the atom is empty space, most of the alpha particles passed straight through
What was Niels Bohr’s model of the atom?
Bohr proposed that electrons ‘orbit’ the nucleus in fixed shells and are not anywhere in between. Each shell is then a fixed distance from the nucleus
Who proved the existence of the neutron?
James Chadwick proved the existence of neutrons, resulting in a model of the atom which is used today
What process would we use to separate a mixture of liquids?
Fractional distillation
What could be a disadvantage of fractional distillation?
Liquids with similar boiling points could be difficult to separate out individually
What is another term for electron shells ?
Energy Levels
