Chemistry atomic structure and the periodic table 1

imported from Quizlet information from pmt

Alkali metals

The elements in Group 1 of the periodic table.

Atom

The smallest part of an element that can exist. All substances are made up of atoms.

Atomic nucleus

Positively charged object composed of protons and neutrons at the centre of every atom with one or more electrons orbiting it.

Atomic number

The number of protons in the nucleus.

Chromatography

A separation technique used to separate a mixture of chemicals by distributing the components between two phases.

Compound

A substance made up of two or more types of atoms chemically combined together.

Crystallisation

A separation technique used to produce solid crystals from a solution by evaporating the solvent.

Displacement

A chemical reaction in which a more reactive element displaces a less reactive element from its compound.

Electron

Negatively charged subatomic particle which orbit the nucleus at various energy levels. Very small relative mass (negligible).

Electron shell

Different energy levels in atoms occupied by electrons.

Element

A substance made up of only one type of atom.

Filtration

A separation technique used to separate solids from liquids.

Fractional distillation

A method of separating a mixture of substances according to their different boiling points.

Group (periodic table)

The columns of the periodic table represent different groups of elements. Elements with similar properties are in the same group.

Halogens

The elements in Group 7 of the periodic table.

Ion

An atom or molecule with an electric charge due to the loss or gain of electrons.

Isotope

Atoms of the same element with the same number of protons but a different number of neutrons.

Mass number

The total number of protons and neutrons in the nucleus.

Metals

Elements that react to form positive ions. Found to the left and towards the bottom of the periodic table.

Mixture

A mixture consists of two or more elements or compounds not chemically combined together.

Neutron

Neutral subatomic particle present in the nucleus of the atom. Relative mass of 1.

Noble gases

The elements in Group 0 of the periodic table.

Non-metals

Elements that react to form negative ions. Found towards the right and top of the periodic table.

Nuclear model

The nuclear atomic model stated that the mass was concentrated at the centre of the atom and that the nucleus was charged.

Periodic table

Table of elements arranged in order of atomic number and such that elements with similar properties are in the same column (group).

Plum pudding model

Atomic model devised after the discovery of the electron. The model suggests the atom is a ball of positive charge with negative electrons scattered through it.

Proton

Positively charged subatomic particle present in the nucleus of the atom. Relative mass of 1.

Relative atomic mass

An average value that takes account of the abundance of the isotopes of the element.

Simple distillation

A procedure by which two liquids with different boiling points can be separated.

Transition metals

The collection of metallic elements in the middle of the periodic table.

Atoms

Atoms make up all substances and are the smallest part of an element that can exist.

Chemical Symbols

Chemical symbols represent an atom of an element e.g. Na represents an atom of sodium.

Compounds

Compounds are formed from elements by chemical reactions. Chemical reactions always involve the formation of one or more new substances, and often involve an energy change.

Fixed Proportions in Compounds

Compounds contain two or more elements chemically combined in fixed proportions and can be represented by formulae using the symbols of the atoms from which they were formed e.g. HCl is a compound containing 1 atom of hydrogen and 1 of chlorine per molecule.

Separation of Compounds

Compounds can only be separated into elements by chemical reactions.

Mixture

A mixture consists of two or more elements or compounds not chemically combined together. The chemical properties of each substance in the mixture are unchanged.

Separation of Mixtures

Mixtures can be separated by: filtration, crystallisation, simple distillation, fractional distillation and chromatography. These are physical processes, so do not involve chemical reactions and no new substances are made.

First model of the atom

Atoms were thought to be tiny spheres that could not be divided.

Plum pudding model

Atom is a ball of positive charge with negative electrons embedded in it.

Alpha particle scattering experiment

Conclusion that the mass of an atom was concentrated at the centre (nucleus) and that the nucleus was charged.

Scattering experiment

A beam of alpha particles was aimed at very thin gold foil and their passage through was detected.

Alpha particle deflection

Some of the alpha particles emerged from the foil at different angles, and some even came straight back.

Repulsion of alpha particles

The positively charged alpha particles were being repelled and deflected by a small concentration of positive charge in the atom (nucleus).

Neil Bohr's suggestion

Suggested electrons orbit the nucleus at specific distances (supported by experimental data).

Later experiments on nucleus

Positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge (protons).

James Chadwick's work

Provided the evidence to show the existence of neutrons within the nucleus.

Atomic number

The number of protons in an atom of an element.

Protons in elements

All atoms of a particular element have the same number of protons.

Different elements

Atoms of different elements have different numbers of protons.

Relative charge of proton

1

Relative charge of neutron

0

Relative charge of electron

-1

Overall charge of an atom

0, so number of protons = number of electrons

Size of atoms

Atoms are very small (radius of about 0.1 nm)

Radius of a nucleus

Less than 1/10,000 of that of the atom, though it holds almost all of the mass

Relative mass of proton

1

Relative mass of neutron

1

Relative mass of electron

Very small

Mass number

The sum of the protons and neutrons in an atom

Isotopes

Atoms of the same element with different numbers of neutrons

Relative atomic mass

An average value that takes account of the abundance of the isotopes of the element

Example question for relative atomic mass calculation

Carbon has 2 isotopes: carbon-14 with abundance 20% and carbon-12 with abundance 80%. Calculate the relative atomic mass of carbon.

Calculation formula for relative atomic mass

((isotope 1 mass x abundance) + (isotope 2 mass x abundance)) ÷ 100

Example calculation for carbon

((14 x 20) + (12 x 80)) ÷ 100 = 1240 ÷ 100 = 12.4

Electronic structure

Electrons occupy the lowest available energy levels (the shells closest to the central nucleus)

Electronic structure of an atom

Tells you how many electrons are in each shell, e.g., for sodium: 2 electrons in shell 1, 8 in shell 2, 1 in shell 3

Electronic structure representation

2,8,1