Atoms, Elements And Compounds Flashcards
What is an atom?
The smallest part of an element that can exist
How are compounds formed?
By chemical reactions of elements
Chemical reactions always involve…
The formation of one or more new substances
What do compounds contain?
Two or more elements chemically combined in fixed proportions
A mixture consists of…
Two or more elements or compounds not chemically combined together
How can mixtures be seperated?
By physical processes (eg filtration, crystallisation, simple/ fractional distillation, and chromatography)
What causes scientific models to be changed or replaced?
New experimental evidence
What were atoms thought to be before the discovery of electrons?
Tiny spheres that could not be divided
The discovery of the electron led to…
The plum pudding model
What did the plum pudding show?
That an atom is a ball of positive charge with negative charge embedded in t
The results from the alpha particle scattering experiment led to the conclusion that…
The nucleus was charged
How did Niels Bohr adapt the nuclear model?
By suggesting that electrons orbit he nucleus at specific distances
The relative charge kids proton is
+1
The relative charge of a neutron is
0
The relative charge of an electron is
-1
The number of electrons is
Equal to the number of protons in the nucleus (atoms have no overall charge)
Atomic number=?
The number of protons in an atom of an element
Atoms have a radius of about
0.1 nm
The radius of a nucleus is
Less than 1/10,000 of that of the atom
The relative masses of
Proton: 1
Neutron: 1
Electron: very small
The mass number is…
The sum of the protons and neutrons in an atom
Isotopes are
Atoms of the same element that have a different number of neutrons
What is the relative atomic mass?
He average value that takes amount of the abundance of the isotopes of that element
The element in the periodic table are arranged in order of…
Atomic number so that elements with similar properties are in columns, aka groups
Before the discovery of protons, neutrons and electrons, scientists ordered elements in order of their
Atomic weight
How did the lack of knowledge on elements affect the arrangement of the early periodic table?
The table was incomplete and some elements were placed in inappropriate groups if the strict order of atomic weights was followed
How did Mendeleev overcome problems with the early periodic table?
Left gaps for elements he thought had not been discovered and in some places changed the order based on atomic weights
What are metals?
Elements that react to form positive ions
What are non-metals?
Elements that do not form positive ions
What are the group 0 elements known as and what are their properties?
The noble gases. Unreactive, and all have 8 electrons on their outer shell (except helium, which has 2 electrons)
Why don’t noble gases easily form molecules?
Their atoms have stable arrangements of electrons
The boiling points of the noble gases increase as…
You go down the group (increasing relative atomic mass)
