Topic 1: Atomic Structure and The Periodic Table Flashcards
(35 cards)
What did John Daltons (English chemist 1766-1844) atomic theory include?
He said that:
- all matters are made up of tiny particles called atoms.
- atoms are tiny hard spheres that cannot be broken down into smaller parts.
- atoms cannot be created or destroyed.
- the atoms in an element are all identical (but each element has its own type of atom)
This theory explained some of the properties of matter.
What happened in the late 19th century when a high voltage was applied to a glass tube that had most air removed?
When a high voltage is applied to a glass tube that has most air removed, glowing rays are seen. Some scientists thought these were ‘cathode rays’ where atoms leaving the negative electrode.
In 1897 what did JJ Thompson discover?
He investigated the mass of particles in the rays and found that they were about 1800 times lighter than the lightest atom -hydrogen. Cathode rays therefore did not contain atoms but subatomic particles, which we now called electrons.
What are the current subatomic particles that make up the structure of an atom?
Scientists have now worked out that atoms are made up of electrons heavier subatomic particles called protons and neutrons. All these particles have very small masses and electric charges. Most of the atom is empty space as the mass is concentrated in the centre of the nucleus.
What are the charges and relative masses of the subatomic particles?
Proton: charge= +1 (positive)
mass= 1
Neutron: charge= 0 (no charge)
mass= 1
Electron: charge= -1 (negative)
mass= almost 0
What is the structure of an atom?
At the centre of an atom is a tiny nucleus containing protons and neutrons. This is surrounded by fast moving electrons arranged in electron shells at different distances from the nucleus.
Why are atoms of the same element always neutral?
Atoms in the same element always have equal numbers of protons and electrons and so have no overall charge because the charges cancel out.
What did Earnest Rutherford discover in 1909?
He was working to investigate the structure of atoms. In one experiment tiny positive particles were fired at a thin gold foil. To their surprise most the particles passed through the gold foil with a few being deflected and a very small number bouncing back. Rutherford explained this by suggesting atoms are mostly empty space, with a small positive central nucleus which contains most of the mass.
How is the periodic table ordered?
The elements were originally placed in order of masses of their atoms. However this caused some elements to be grouped with others of very different products. So a few elements were swapped around to make sure that those with similar properties were grouped together, even if it meant they were no longer in the correct order of mass.
What experiments did Henry Moseley carry out and how is this affect the order of the periodic table?
Experiments carried out by him confirmed that the rearranged order of elements were actually correct. He showed they were in order of of the amount of positive charge in the nucleus
What is the order of the modern periodic table?
In 1918 the proton was discovered. The modern periodic table places the elements in order of the number of protons in their atoms. This is the atomic number and it is this that defines an element - all the atoms of a particular element have the same unique atomic number (even their isotopes).
Increasing atomic number.
What is the mass number?
The mass of an electron is described as negligible (it is so small it can be ignored). This explain why the nucleus of any atom contains nearly all its mass. For this reason the total number of protons and neutrons in an atoms is called the mass number.
What represents the mass number and how is it different to the atomic number?
It is the top number and is the amount of neutrons and protons combined.
The atomic number is also known as the proton number and is just the number of protons. It is the bottom number underneath the mass number.
What did James Chadwick discover in 1932 and what did this explain?
He discovered the neutron. His discovery explained why some atoms of the same element have different masses. These atoms are isotopes. They have the same atomic number but different mass numbers.
What is an isotope and how do we refer to it?
Atoms of the same element that have different mass numbers but the same atomic number.
We refer to a specific isotope by adding its mass number to the element’s name.
How did neutrons lead to the discovery of nuclear energy?
Understanding neutrons lead to the discovery of nuclear energy by firing neurones at the isotope uranium-235. It was discover nucleus can be split (nuclear fission). This produces energy new elements and transfers large amounts energy. Nuclear power stations use the energy from fission to produce electricity.
What are relative atomic masses?
The mass of an atom is incredibly small so we measured it relative to an atom of Carbon-12. The isotope is used as a standard and given a mass of exactly 12.
What is the relative mass of an isotope?
The relative mass of an isotope is its mass number.
How do you calculate the relative atomic mass of an atom?
The symbol is Ar. A relative atomic mass is the mean mass of an atom of an element compared with carbon 12. It takes into account all the isotopes of an element and the amounts of each. RAMs are not whole numbers but most values are commonly rounded to whole numbers. The RAM of an element and its atomic number are shown in the periodic table
Wh invented the Periodic table?
In 1869 Dimitri Mendeleev was a Russian scientist who was writing a chemistry text book and constructed the table to help make sense of the elements.
How did Mendeleev first order the periodic table?
In order of of increasing relative atomic mass. Unlike other chemists who tried it before he left gaps to filled in later.
Why did Mendeleev swap some positions of elements?
He swapped them if he thought that it better suited their chemical properties and those of their compounds.
E.g iodine has a lower RAM than tellurium so he should have placed it before tellurium due to its physical properties. Instead he placed it after tellurium so that it lines up with fluorine, chlorine and bromine as they were elements with similar chemicals properties to iodine.
Why did Mendeleev leave gaps?
He assumed that elements would continue to be discovered, so he left gaps for them. This helped him to position existing so that vertical columns contained elements with increasing relative atomic mass, and horizontal rows contained elects with similar chemical properties.
What predictions did he make about undiscovered elements?
He used gaps in the table to make predictions about the properties of undiscovered elements, based on the properties of nearby elements.
