Leaving Cert Chemistry Term Flashcards
Dalton’s Atomic Theory
- All matter is made up of very small particles called atoms.
- All atoms are indivisible. They cannot be broken down into simpler particles.
Cathode rays
Streams of negatively charged particles called electrons. They travel in a straight lines from the cathode to the anode, are deflected by electric and magnetic fields, and have sufficient energy to move a small object such as a paddle wheel.
Element
A substance that cannot be split into simpler substances by chemical means
Dobereiner’s Triad
A group of 3 elements with similar chemical properties in which the atomic weight (relative atomic mass) of the middle element is approximately equal to the average of the other two.
Newlands Octaves
Arrangement of elements in which the first and eighth element, confusing from a particular element have similar properties
Mendeleev’s Periodic Law
When elements are arranged in order of increasing atomic weight (relative atomic mass), the properties of the element recur periodically
Atomic number
The number of protons in the nucleus of that atom
Modern Periodic TABLE
An arrangement of elements in order of increasing atomic number
Modern Periodic LAW
When elements are arranged in order of increasing atomic number, the properties of the elements recur periodically, .ie the properties displayed by an element are repeated at regular intervals in other elements
Mass number
The sum of the number of protons and neutrons in the nucleus of an atom of that element
Isotopes
Atoms of the same element which have different mass numbers due to the different number of neutrons in the nucleus
Relative atomic mass
The average of the mass numbers of the isotopes of the elements as they occur naturally.
Taking their abundances into account.
Expressed on a scale in which the atoms of the carbon 12 isotope have a mass of exactly 12 units
Compound
A substance that is made up of two or more different elements combined together chemically
Octet Rule
When bonding occurs atoms tend to reach an electron arrangement with eight electrons in the outermost energy level
Ion
A charged atom or group of atoms
Ionic bond
The force of attraction between oppositely charged ions in a compound. Ionic bonds are always formed by the complete transfer of electrons from one atom to another.
Molecule
A group of atoms joined together the smallest particle of an element or compound that can exist independently
Valency
The number of bonds the atom of an element forms when it reacts
Electronegativity
The relative attraction that an atom in a molecule has for the shared pair of electrons in a covalent bond
Polar covalent bond
A bond in which there is unequal sharing of the pair of electrons. This causes one end of the bond to be slightly positive and the other end slightly negative
Intramolecular forces
Bonding takes place within a molecule, i.e it holds the atoms together. Covalent bonding and polar covalent bonding are examples of intramolecular bonding
Intermolecular forces
The forces of attraction that exist between molecules. Van der Waals forces, dipole-dipole forces and hydrogen bonding are examples of intermolecular forces
Van der Waals forces
Weak attractive forces between molecules resulting from the formation of temporary dipoles. They are the only forces of attraction between non-polar molecules
Mole
Th amount of that substance that contains 6 x 10*23 particles of that substance
Dipole-dipole forces
Forces of attraction between the negative pole of one polar molecule and the positive pole of another polar molecule
Hydrogen bonds
Type of dipole-dipole attractions between molecules in which hydrogen atoms are bonded to nitrogen, oxygen or fluorine. The hydrogen atom carries a partial positive charge and is attracted to thr electronegative atom in another molecule. Thus, the hydrogen bond acts as a bridge between two electronegative atoms in separate molecules
Law of Conservation Mass
The total mass of the products of a chemical reaction is the same as the total mass of the reactants
Law of Conservation of Matter
In any chemical reaction, matter is neither created nor destroyed but merely changed from one form into another
Relative molecular mass
The average mass of one molecule of that compound compared with one twelfth of the mass of one atom of the carbon-12 isotope.
Gas
A substance that has no well-defined boundaries but diffuses rapidly to fill any container in which its placed
Boyle’s Law
At constant temperature, the volume of a fixed mass of gas is inversely proportional to its pressure
pV= K
Charles’ Law
At constant pressure, the volume of a fixed mass of gas, is directly proportional to its temperature measured on the Kelvin Scale
V/T = k
Gay-Lussac’s Law of Combining Volumes
In a reaction between gases, the volumes of the reacting gases and the volumes of any gaseous products are in the ratio of small whole numbers provided the volumes are measured at the same temperature and pressure.
Avogadro’s Law
Equal volumes of gases contain equal numbers of molecules under the same conditions of temperature and pressure
Ideal gas
A gas that perfectly obeys all the assumptions of the kinetic theory of gases under all conditions of temperature and pressure.
Real gas
Differ from ideal gases because.
i) Forces pf attraction and repulsion do exist between the molecules and
ii) the volume of the molecule is not negligible
Arrehnius’ definition of an acid
A substance that dissociates in water to produce H+ ions
Arrhenius’ definition of a strong acid
A substance that almost completely dissociates in water to produce hydrogen (H+) ion
Arrhenius’ definition of a weak acid
A substance that only slightly dissociates in water to give hydrogen ions
Arrhenius’ definition of a base
A substance that dissociates in water to produce hydroxide ions
Arrhenius’ definition of a strong base
A substance that almost completely dissociates in water to give hydroxide ions
Arrhenius’ definition of a weak base
A substance that only slightly dissociates in water to produce hydroxide ions
Brønsted-Lowry’s definition of a strong acid
A good proton donor
Brønsted-Lowry’s definition of a weak acid
A poor proton donor
Brønste Lowry’s definition of a strong base
A good proton acceptor
Brønsted-Lowry’s definition of a weak base
A poor proton acceptor
Conjugate acid base pair
Any pair consisting of an acid and a base that differ by one proton
Salt
The substance formed when the hydrogen ion from an acid is replaced by a metal or an ammonium ion
Neutralization
The reaction between an acid and a base to form a salt and water
Solution
A completely perfect mixture of a solute and a solvent. In a solution the particles of the solute are uniformly distributed throughout the solvent
Molarity
The number of moles of solute per litre of solution
Standard solution
A solution whose concentration is accurately known
Primary standard
A substance that can be obtained in a stable, pure and soluble solid form so that it can be weighed out and dissolved in water to give a solution of accurately known concentration
Titration
A laboratory procedure where a measured volume of one solution is added to a known volume of another solution until the reaction is complete
Energy level
The fixed energy value that an electron in an atom may have
Ground state
The electrons occupy the lowest available energy levels
Excited state
The electrons occupy a higher energy levels than those available in the ground state
Heisenbergs Uncertainty Principle
It’s impossible to measure at the same time both the velocity and the position of an electron
Sublevel
A subdivision of a main energy level and consists of one or more orbitals of the same energy
Principles of mass spectrometry
Charged particles moving in a magnetic field are deflected to different extents according to their masses and are thus separated according to these masses
Electron configuration
Shows the arrangement of electrons in an atom of an element
Aufbau Principle
When building up the electron configuration of an atom in its ground state the electrons occupy the lowest available energy levels
Hund’s Rule of Maximum Multiplicity
When two or more orbitals of equal energy are available the electrons occupy them singly before filling them in pairs