The Atom: Basic Building Block Of All Matter Flashcards
Who were six scientists who were influential to our understanding of the atom?
Democritus Dalton Thomson Rutherford Chadwick Bohr
What was Democritus’ atomic theory?
That matter is made up of small basic particles
What did Dalton’s model of matter state?
All matter is made up of indestructible and indivisible atoms
Atoms of the same element are identical
Atoms of different elements differ from one another
What was Dalton’s model based on?
The knowledge that elements combine in fixed mass ratios
What was a shortcoming of Dalton’s model of the atom?
He made no reference to the electrical nature of matter
What did Thomson discover about atoms?
He explored electrons
What did Thomson discover about electrons?
All electrons are identical
Substances differ because of the number of electrons that they have and how they are arranged
The mass of an electron is about 2000 times less than the mass of protons
How did Thomson think an atom looked?
A solid sphere with positive and negative charges evenly distributed throughout to make the atom neutral
How Thomson research electrons?
He used cathode ray tubes
What is a cathode ray tube?
A tube filled with gas that has a very low pressure
The glass of the tube then becomes fluorescent
What did Rutherford discover about the atom?
The protons of an atom are grouped together in the nucleus
The nucleus is surrounded by “empty” space occupied by electrons
The mass of an atom is concentrated mainly in the nucleus
How did Rutherford make his discovery?
He bounced alpha particles off gold foil
What are alpha particles?
Positively charged particles given off by radioactive substances
What was a shortcoming in Rutherford’s model of the atom?
It could not explain why electrons which move about the nucleus do not spiral inwards towards the nucleus
What did Chadwick discover about atoms?
He discovered the existence of neutrons in the nucleus of an atom
How did Chadwick discover the existence of neutrons?
He bombarded beryllium with alpha particles
Why did Chadwick perform his experiment?
Rutherford’s model could not explain why Helium is four times heavier than Hydrogen, despite only the one difference in the number of protons
What did Bohr contribute to atomic theory?
Electron can move only in fixed, permitted orbits
Therefore, this electron has a definite energy which cannot change while the electron is moving in that particular orbit
What takes up the most space in an atom?
The nucleus
What is the nucleus made out of?
Protons and neutrons
What contributes the most mass to an atom?
The nucleus
Where can the electrons of an atom be found?
In fixed orbits surrounding the nucleus
What are the fixed orbitals of electrons called?
Energy levels
In a neutral atom, what is the relationship between the number of electrons and the number of protons?
They are equal
What is the atomic number of an atom?
The number of protons in an atom
What does the atomic number determine?
The type of element that the atom is
How do we denote the atomic number of an element?
By writing it as a subscript number to the bottom left of the atomic symbol of that element
What is the mass number of atoms?
The mass of an atom
It is found by adding the number of protons and neutrons together
How do you find out how many neutrons are in an atom?
Mass number - atomic number
How do you denote the mass number of an element?
By writing it in the top left hand corner next to its chemical symbol
What is an isotope?
An atom that has the same number of protons that it usually has, but a different number of neutrons
i.e its mass is different
Does an isotope behave differently chemically?
No
What are the atomic masses found on the Periodic Table?
Average masses
How can an atom lose or gain electrons?
Through a chemical reaction
What happens when a neutral atom loses or gains electrons?
It becomes charged
What is an ion?
A charged ion
When does an atom become positively charged?
When it loses an electron
It will now have more protons than electrons
When will an atom become negatively charged?
When it gains an electron
It will now have more electrons than protons
What is a cation?
A positively charged ion
What is an anion?
A negatively charged ion
What symbol can be used to denote a proton?
Z
What symbol can be used to denote neutrons?
N
What is the formula for atomic mass?
Atomic Mass = Z + N
When an electron is moving in an energy level, can it emit or absorb energy?
No
When does an electron emit energy?
When it falls to a lower energy level
When does an electrons absorb energy?
When it jumps to a higher energy level
What does it mean to say that energy radiated or absorbed by electrons is quantised?
It is limited to certain energy values determined by the energy difference between the energy levels
What does the wave model do?
Determines the general region or area where an atom will be found
What is an orbital?
A region in space where the probability of finding an electron is greatest
What are the two main types of orbitals?
S
P
What is the shape of an s-Orbital?
Spherical
How are s-Orbitals arranged?
Symmetrically around the nucleus
They differ in size
How many s-Orbitals occur in each energy level?
One
What is the shape of p-Orbitals?
They are dumbbell in shape
How are p-Orbitals arranged?
In groups of three
At right angles to one another
What are the three types of p-Orbitals called?
X- horizontal
Y- Vertical
Z- diagonal
Where are p-Orbitals found?
From the second energy level onwards
What is the Afbau principle used for?
To determine how electrons occupy the orbitals of an atom
What preference do electrons have when occupying orbitals?
They always occupy the orbitals having the lowest possible energy values
Which orbitals have the lowest possible energy levels?
The ones closest to the nucleus
What does Pauli’s Exclusion Principle say?
That each orbital can contain a maximum of two electrons provided they spin in opposite directions
Why do electrons spin in opposite directions?
The two negatively charged particles repel one another
What does Hund’s Rule say?
No p-orbital will have two electrons in it until all the p-orbitals in that energy level have at least one electron
What are core electrons?
Electrons found in the inner, full energy levels
What are valence electrons?
The electrons in the outermost energy level
What does an Afbau diagram look like?
Number of energy levels shown by a number on the y-axis
Orbitals shown by blocks
Electrons shown by arrows pointing in opposite directions
Type of orbital shown by a letter beneath the block
What is electron configuration?
A type of notation showing the position of electrons
What does electron configuration look like?
Number of energy level
Type of orbital
Superscript number denoting the number of electrons
