Chapter 2 - Atoms, elements and compounds Flashcards
What is an element?
An element is a substance made of atoms that all contain the same number of protons and cannot be split into anything simpler.
What is a compound?
A compound is a pure substance made up of two or more elements chemically combined. They cannot be separated into their elements by physical means.
What is a mixture?
A mixture is a combination of two or more substances that are not chemically combined. They can be separated by physical methods.
What is an atom?
An atom is made of subatomic particles called protons, neutrons and electrons. The protons and neutrons are located at the centre of the atom called the nucleus. The electrons move very fast around the nucleus in orbital paths called shells.
What are the relative masses and charges of the three subatomic particles?
What is the atomic number / proton number?
The atomic number (proton number) is the number of protons in the nucleus of an atom. It is also the number of electrons present in a neutral atom and determines the position of the element on the periodic table.
What is the nucleon number / mass number?
The nucleon number (mass number) is the total number of protons and neutrons in the nucleus of an atom. The neutron number minus the proton number gives you can number of neutrons of an atom.
How do you work out the nucleon number / mass number?
mass number = number of protons + number of neutrons
How do you work out the number of protons?
number of protons = mass number – number of neutrons
How do you work out the number of neutrons?
number of neutrons = mass number – number of protons
How do you work out the number of electrons?
An element will have the same number of electrons and protons.
How does the groups (vertical) and periods (horizontal) show the structure of an atom?
The number of electrons in the valence shell is equal to the group and the number of shells is equal to the period.
What are electron shell diagrams?
Electron shell diagrams show the number of electrons orbiting the nucleus in shells. The further away from the nucleus, the more energy a shell has. The first shell can hold 2 electrons, the second shell can hold 8 electrons, and the third shell can hold 8 electrons.
What group has a full outer shell?
Group 8 noble gases have a full valence (outer) shell, meaning they are unreactive.
What are isotopes?
Isotopes are different atoms of the same element that have the same number of protons but a different number of neutrons. They have the same chemical properties as the original element because they have the same number of electrons and therefore the same electronic configuration.
What is relative atomic mass?
Relative atomic mass is the average mass of all the isotopes of that element.
What is the formula for relative atomic mass?
What is an ion?
An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons.
What are positive ions?
Positive ions are known as cations and are formed when an atom loses an electron.
What are negative ions?
Negative ions are known as anions and are formed when an atom gains an electron.
What is an ionic bond?
An ionic bond is a strong electrostatic attraction between oppositely charged ions (metals and non-metals). Metals lose their outer electrons, forming positive ions (cations) and non-metals gain these outer electrons, forming negative ions (anions), both forming a full shell.
What is the structure of an ionic compound?
Ionic compounds have a giant lattice structure. A giant lattice structure is a regular arrangement of alternating positive and negative ions.
What are the characteristics of ionic compounds in terms of melting points, boiling points and electrical conductivity?
Ionic compounds have high melting and boiling points because they have giant structures and strong electrostatic forces of attraction between oppositely charged ions in all directions. These forces require a lot of energy to break. They are poor conductors in the solid state as the ions are in fixed positions in the lattice and unable to move to carry a charge. They are good conductors of electricity in molten or aqueous as when the compound it melted or dissolved, the ions are able to move and carry a charge.
What are dot and cross diagrams?
Dot and cross diagrams show the arrangement of the outer shell electrons in an ionic or covalent compound. The charge on each ion is written at the top right-hand corner.
What are covalent bonds?
Covalent bonds are formed when a pair of electrons is shared between two atoms leading to noble gas electronic configurations. Covalent bonds occur between two non-metals.
How do you write the formula of covalent compounds?
If a covalent bond only shares one pair of electrons (2 electrons) it will be represented by a single dash. If it shares two pairs of electrons (4 electrons) it will be represented by two dashes.
What are the characteristics of covalent compounds in terms of melting points, boiling points and electrical conductivity?
Covalent compounds have low melting and boiling points as there are only weak intermolecular forces acting between the molecules. They are poor conductors as there are no free ions or electrons to carry the charge.
What are two giant covalent structures?
Graphite and diamond
What is the covalent bonding in graphite?
Each carbon atom in graphite is bonded to three others, forming a layer of hexagons, leaving one free electron per carbon atom which becomes delocalised. The covalent bonds within the layers are very strong but the layers are attracted to each other by weak intermolecular forces.
What is the covalent bonding in diamond?
In diamond, each carbon atoms bonds with four other carbon atoms, forming a tetrahedron. All covalent bonds are identical, very strong and there are no intermolecular forces.
How are diamond and graphite similar?
Diamond and graphite are allotropes of carbon which have giant covalent structures. Both substances contain only carbon atoms but due to the differences in bonding arrangements they are physically completely different.
What are the characteristics of graphite in terms of melting point, feel and uses?
Graphite conducts electricity as there is a delocalised electron that is free to move through the structure and carry charge. It has a high melting point due to the high amount of energy needed to break the strong covalent bonds. It is slippery as there are weak intermolecular forces between them allows them to slide over each other. Graphite can be used as a lubricant or an electrode.
What are the characteristics of diamond in terms of melting point, feel and uses?
Diamond have a very high melting point as the covalent bonds require a lot of energy to break. It is extremely hard and dense as each carbon atom is bonded to four other carbon atoms. Diamonds can be used it cutting tools like drills.
What is the covalent bonding in silicon(IV) oxide?
Silicon(IV) oxide is a macromolecular compounds which occurs naturally as sand and quartz. Each oxygen atom forms covalent bons with 2 silicon atoms and each silicon atoms in turn forms covalent bonds with 4 oxygen atoms. This forms a tetrahedron.
What are the characteristics of silicon(IV) oxide in terms of feel, boiling point, solubility and electrical conductivity?
Silicon dioxide has lots of very strong covalent bonds and no intermolecular forces, so it has similar properties to diamonds. It is very hard and have a very high boiling point, it is insoluble in water and does not conduct electricity.
What is metallic bonding?
Metallic bonding is the electrostatic attraction between the positive ions in a giant metal lattice and a ‘sea’ of delocalised electrons.
What are the characteristics of metals in terms of heat and electrical conductivity and malleability?
Metals are good conductors of heat and electricity because the delocalised electrons are free to move and carry a charge though the whole structure. Most metals are malleable meaning they can be hammered into shape. This is because they are arranged in layers which can slide over each other when force is applied.
