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