Atomic structure Flashcards
What is an atom?
An atom is the smallest part of
an element that can exist. Atoms of each element are represented by a chemical symbol, eg
O represents an atom of oxygen, Na represents an atom of sodium.
what is a compound?
Compounds are formed from elements by chemical reactions.
Chemical reactions always involve the formation of one or more new substances, and often involve a detectable energy change.
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.
Compounds can only be separated into elements by chemical reactions
what is a 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.
how can mixtures be separated? (go over these using videos and posters)
Mixtures can be separated by physical processes such as filtration, crystallisation, simple distillation, fractional distillation and chromatography. These physical processes do not involve chemical reactions and no new substances are made
what was theory before the discovery of the electrons?
Before the discovery of the electron, atoms were thought to be tiny spheres that could not be divided.
What was the plum pudding model?
The plum pudding model suggested that the atom is a ball of positive charge with negative electrons embedded in it. - J.J Thompson 1904
What was the gold alpha particle experiment?
The results from the alpha particle scattering experiment led to the
conclusion that the mass of an atom was concentrated at the centre
(nucleus) and that the nucleus was charged
What was Neil Bohr’s theory?
Niels Bohr adapted the nuclear model by suggesting that electrons orbit the nucleus at specific distances. The theoretical calculations of Bohr agreed with experimental observations
What did James Chadwick do?
Later experiments led to the idea that the positive charge of any nucleus could be subdivided into a whole number of smaller particles, each particle having the same amount of positive charge.
The name proton was given to these particles.
The experimental work of James Chadwick provided the evidence to show the existence of neutrons within the nucleus. This was about 20 years after the nucleus became an accepted scientific
idea.
What is relative charge of an electron?
-1
what is the relative charge of a proton?
+1
what is the relative charge of a neutron?
0
What is the atomic number?
The number of protons in an atom of an element is its atomic number. All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of
protons.
relative mass of a proton
1
relative mass of a neutron
1
relative mass of an electron
very small
what is a mass number?
The sum of the protons and neutrons in an atom is its mass number
what is an isotope?
Atoms of the same element can have different numbers of neutrons; these atoms are called isotopes of that element.
What is the relative atomic mass?
The relative atomic mass of an element is an average value that takes account of the abundance of the isotopes of the element.
How is the periodic table arranged?
The elements in the periodic table are arranged in order of atomic (proton) number and so that elements with similar properties are in columns, known as groups. The table is called a periodic table because similar properties occur at regular intervals
what do elements in the same group have?
Elements in the same group in the periodic table have the same number of electrons in their outer shell (outer electrons) and this gives them similar chemical properties.
How was the periodic table originally arranged?
Before the discovery of protons, neutrons and electrons, scientists attempted to classify the elements by arranging them in order of their atomic weights.
Why were the early periodic tables incomplete?
The early periodic tables were incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed.
How did Mendeleev impact periodic tables?
Mendeleev overcame some of the problems by leaving gaps for elements that he thought had not been discovered and in some places changed the order based on atomic weights.
Elements with properties predicted by Mendeleev were discovered and filled the gaps.
Knowledge of isotopes made it possible to explain why the order based on atomic weights was not always
correct.