Chemistry Unit 1

Aristotle

- 330 bc - stated that matter was made up of four elements fire, air water and earth

Democritus

- 470 bc - First proposed that matter was made of atoms - Proposal was rejected because of Aristotle argued against it because Aristotle was a highly regarded philospher it wasnt taken into account

Ion

- A charged atom by either losing or gaining elctrons via chemical reactions

Mendeleev

- Arragned the known elements of that time based on their atomic mass and chemical properties - Elements with similar properties we in periods - Had left gaps because he had predicted that undiscovered elements would fit in those gaps and had successfully predicted many of their properties

Molecular Mass

- As it increases then viscosity of the liquid will also increase

Quantum-mechanical model

- Complicated mathematical model of the atom - Proposed that electrons exist in regions of space called orbitals - these orbitals exist in a complex array of energy levels around the nucleus

Plum-pudding model

- Created by Thomson - A shpere which contains positive matter in which electrons are embedded - hence the name the plum are like the electrons

Electron Configuration

- Elements within the same group have the same outer shell electron configuration and exhibit nearly the same chemical properties

Rutherford Model

- Explain it to be like the solar system - Were the electrons orbit the nucleus like the planets orbit the Sun

Bohr

- In 1913 had proposed that electrons move around the nucleus of the atom in certain fixed paths, called orbits - shells have different energy levels - His hypothesis was to explain the emission spectra

Gold foil experiment

- In the gold foil experiment they bombarded thin gold foil with postively charged alpha particles which was expected that all particles would go straight through - Although about one in every 10 000 had bounced back

Atomic Subshells

- Is the sub-division of shells - Different energy levels - Goes accordingly s, p, d and f

Thomson

- Produces the plum-pudding model - Stated that atoms were postively charge matter which eletrons were embedded - Used the cathode-ray tube experiment - therefore suggesting that electrons must be part of the atom and if atoms had a neutral charge overall he suggested there must also be positive charges also - challenged daltons theory that atoms were the smalled particles

Relative Atomic Mass

- The average atomic mass of all the isotopes of the that element when taking into account their abundances

Periods

- The horizontal rows in the periodic table - is defined by the outter most shell

Melting point

- The temperature at which a given solid will melt. - melting point increases with an increase in the number of electrons in the outter shell - increases as you move down a group

Rutherford

- Used radioactivity to test Thomsons plum pudding model - Used the gold foil experiment - To explain these observations Rutherford had suggested that the mass of the atom and the positive charges were concentrated into a small, dense positively charged nucleus which electrons orbit around - Created the nuclear model of atomic structure

Groups

- Vertical columns in the periodic table - based on their chemical properties - All elements have the same outer shell configuration

Excited state

- When electrons have become excited by either heat or electricity - Were the electron becomes higher then its normal energy level - Electrons move to a higher energy level

Elements

- a molecule composed of one kind of atom; cannot be broken into simpler units by chemical reactions.

Radio-activity

- emitting radioacitivity spontaneously - caused by nucleus' which are unstable

Atomic Radius

- generally increases down a group - generally decreases from left to right in a period - the size on the atom - cannot be measured directly - as the number od positive charges in the nucleus increase, the nuclear charge increases also.

Electronegativity

- is a measure of degree to which an atom can attract an eletron to itself - in a period left to right the electronegativity increases - moving down a group the electronegativity decreases

Ionisation energies

- is the amount of energy needed to tear an electron away from the atom

Relative isotopic mass

- is the atomic mass of each element isotope

Atomic Mass

- is the number of protons and neutrons in a specific element - can be discovered if you know the atomic mass

Atomic Number

- is the number of protons in a atom - goes accordinly on a periodic table

Emission Spectra

- produced by the light emitted by a once excited electron of the element - is produced by gases - The emission lines correspond to photons of discrete energies that are emitted when excited electrons make transitions back to lower-lying levels (ground state)

Sub-atomic particles

- protons have a positive charge and are found inside the nucleus - Neutrons have a neutral charge and are found in the nucleaus - Electrons are the same amount of protons and are found outside the nucleaus within the shells

Orbitals

- regions around the nucleus in which given electron or electron pair is likely to be found - electron like to be in pairs - therefore orbitals contain half the number of electron in which a shell s,p, d and f can hold - orbitals are within the subshell

The Flame test

- shows that as when electron moves from a lower engery level to a higher (excited state) due to being excited from electricity or from a flame - when it falls back down to its original level (ground state) energy is released in the form of a colour from the emission spectrum

First ionization energy

- the energy required to remove the outtermost electron - Is the energy required to remove an electron from a gaseous atom - increases from left to right through a period - takes little energy to ionise an atom in group 1 - takes alot of energy to ionise an atom in groups 16 - 17 this occurs as the core charge increases across a period

Ground State

- the lowest energy state of an atom, molecule, particle - lower-lying levels

Shells

- the regions of an atom that are occupied by electrons - First shell : 2 electrons. Second Shell: 8 electrons.Next 8

Isotope

- when and element has the same atomic number but a different amount of neutrons - different forms of an element, with the same atomic number but varying atomic masses

Cathode-ray tube experiment

- which he discovered that electrons which made the cathode ray tube could be deflected by mangets or electrically charged plates - Regardless of the different gases or metal plates he discovered that same charge-to mass ration was obtained - therefore suggesting that electrons must be part of the atom and if atoms had a neutral charge overall he suggested there must also be positive charges also

Model of an atom

the model of an atom is a representation of what it is composed of and how they are related to each other on the basis of experimentation and evidence