C4 Flashcards
When and what was John Dalton’s theory?
In 1800, he proposed the theory that all atoms of the same element were the same.
When and what was J.J.Thomson’s discovery?
In the late 1890s, he discovered the electron
When and what was Ernest Rutherford’s discovery?
In 1911, he discovered that the atom had a dense centre called the nucleus.
When and what was Niels Bohr’s prediction?
In 1913, he predicted that electrons occupy orbitals.
What have some unexpected results from scientists such as Geiger and Marsden led to?
The model of the atom being modified in order to explain them
What is the structure of an atom?
An atom has a central nucleus surrounded by shells of negatively charged electrons. The nucleus is made up of protons and neutrons. The nucleus is positively charged but the atom has no overall charge.
Why does an atom have no overall charge?
Because it has the same number of (positive) protons and (negative) electrons, so the charges cancel each other out
What are the dimensions of an atom?
Atoms have a radius of about 1^-10m and a mass of about 10^-23g
What is the relative charge of a proton?
+1
What is the relative charge of a neutron?
0
What is the relative charge of an electron?
-1
What is the relative mass of a proton?
1
What is the relative mass of a neutron?
1
What is the relative mass of an electron?
0.0005
What is an element?
An element is made of one type of atom. Elements can’t be chemically broken down. There are just over 100 naturally occurring elements
What is a compound?
A compound is a substance made of two or more elements that are chemically combined. You can identify the elements in a compound from its formula, using the periodic table.
What is the mass number?
The total number of protons and neutrons in an atom. It’s the bigger of the two numbers next to the element symbol.
What is the atomic number?
The total number of protons in an atom. It’s the smaller of the two numbers next to the element symbol.
How are the elements in the periodic table arranged?
In increasing atomic number
What can you use the periodic table to find?
An element from its atomic number, and the atomic number of an element
What is the group number the same as?
The number of electrons in the outer shell of an element’s atom.
What is the period number the same as?
The number of occupied shells that an element’s atom has
What do you need to be able to work out the number of protons, electrons and neutrons in an atom?
The atomic number, mass number and charge
What are isotopes?
Atoms of the same element that have the same atomic number but a different mass number
What are the similarities and the difference between isotopes?
They have the same number of protons and electrons, but a different number of neutrons.
What does electron configuration tell you?
How the electrons are arranged around the nucleus in shells. The first shell can hold a maximum of 2 electrons, and the second and outer shell have a maximum of 8.
What is an ion?
A charged atom or group of atoms.
How is a positive ion made?
When an atom, or group of atoms, loses one or more electrons.
How is a negative ion made?
When an atom, or group of atoms, gains one or more electrons.
What happens in ionic bonding?
The metal atom loses all outer-shell electrons to become a positive ion, the non-metal atom gains electrons to fill its outer shell and become a negative ion. The positive and negative ions are attracted to each other. This attraction is an ionic bond.
When can the two ionically bonded compounds, sodium chloride and magnesium oxide, conduct electricity. They don’t conduct electricity when solid because the ions are held in place and can’t move, and both have high melting points.
They both dissolve in water, and can conduct electricity when in solution because the charged ions are free to move about. Both can also conduct electricity when molten because the charged ions are free to move about.
Sodium chloride and magnesium oxide form giant ionic lattices in which positive and negative ions are strongly attracted to each other. What does this mean?
It means that they have high melting points as there is a strong attraction between oppositely charged ions. They can conduct electricity when molten or in solution because the charged ions are free to move about. They don’t conduct electricity when solid because the ions are held in place and can’t move.
Why does magnesium oxide have a higher melting point than sodium chloride?
Because the ionic bonds are stronger and need more energy to be broken.
When a metal and a nonmetal combine, what happens?
Electrons are transferred from one atom to the other, forming ions. Each ion will have a complete outer shell.
What is a stable octet?
A complete outer shell
What do ions with different charges combine to form?
Ionic compounds, which have equal amounts of positive and negative charge.
What is a vertical column of elements in a periodic table called?
A group
Why do elements in the same group in the periodic table have similar chemical properties?
Because they have the same number of electrons in their outer shell.
What is a horizontal row of elements in a periodic table called?
A period.
What is the period for an element related to?
The number of occupied electron shells it has.
If you are given an element’s electronic structure, how do you find its position in the periodic table?
Example: sulfur’s structure is 2.2.6, so it has three electron shells and six electrons in its outer shell. So, it can be found in the third period and in Group 6
What are the three types of bonding?
Ionic, covalent and metallic
What are ionic bonds between?
metals and non-metals
What are covalent bonds between?
non-metals
What are metallic bonds between?
metals only
What is covalent bonding?
It’s when non-metals combine by sharing pairs of electrons. Water and carbon molecules are both covalently bonded molecules.
Why do simple covalently bonded molecules have low melting points?
Because they have weak intermolecular forces of attraction between molecules.
Why don’t simple covalently bonded molecules conduct electricity?
Because there aren’t any free electrons
How is the simple covalently bonded molecule, hydrogen, formed?
the two hydrogens share a pair of electrons
How is the simple covalently bonded molecule, chlorine, formed?
the two chlorine atoms share a pair of electrons
How is the simple covalently bonded molecule, methane, formed?
the carbon atom shares a pair of electrons with each hydrogen atom
How is the simple covalently bonded molecule, carbon dioxide, formed?
The outer shells of the carbon and oxygen atoms overlap. The carbon atom shares two pairs of electrons with each oxygen atom to form a double covalently bonded molecule