Chapter 3 - Atoms, Elements and Compounds Flashcards
What are elements
Elements are made of tiny particles of matter called atoms
What do atoms consist of
Each atom is made of subatomic particles called protons, neutrons and electrons
Their size is so tiny that we can’t really compare their masses in conventional units such as kilograms or grams, so a unit called the relative atomic mass is used
What is relative atomic mass
One relative atomic mass unit is equal to the mass of a carbon-12 atom.
All other elements are measured relative to the mass of a carbon-12 atom and since these are ratios, the relative atomic mass has no units
What is hydrogens relative atomic mass
Hydrogen for example has a relative atomic mass of 1, meaning that 12 atoms of hydrogen would have exactly the same mass as 1 atom of carbon
What is the atomic number/ proton number
The atomic number (or proton number) is the number of protons in the nucleus of an atom. The symbol for this number is Z
It is also the number of electrons present in an atom and determines the position of the element on the Periodic Table
What is the nucleon number
Total number of protons and neutrons in the nucleus of an atom. The symbol for this number is a
What are electrons and what do they do
They are the particles surrounding the nucleus of the atom. They are subatomic particles that move very fast around the nucleus
They move in orbital paths called shells
What are groups in periodic table
Vertical columns consisting of elements with same amount of valence electrons, giving them similar chemical properties.
What are periods in periodic table
Horizontal rows in periodic table
What are isotopes
Isotopes are atoms of the same element that contain the same number of protons and electrons but a different number of neutrons.
What is the symbol of an isotope
The symbol for an isotope is the chemical symbol (or word) followed by a dash and then the mass number.
What are the types of isotopes
Isotopes can be divided into two categories: radioactive and non-radioactive
What are radioactive isotopes
Radioactive isotopes (radioisotopes) are unstable due to the imbalance of neutrons and protons, which causes the nucleus to decay over time through nuclear fission and emit radiation. Though they have many industrial and medical uses.
What are non - radioactive isotopes
Non-radioactive isotopes are stable atoms which really only differ in their mass.
Uses of radioactive isotopes
Radioactive isotopes emit radiation that can kill cells so they are used to treat cancer.
And Radioactive dating uses the carbon-14 isotope to extract carbon-containing materials such as organic matter, rocks and other artefacts.
What is nuclear fission
It’s a nuclear reaction in which a heavy nucleus splits spontaneously or on impact with another particle, with the release of energy
Is radioactive decay a nuclear process or chemical reaction
It’s a nuclear process
What are the ways of representing the structure of the atom
We can represent the structure of the atom in two ways: using diagrams called electron shell diagrams or by writing out a special notation called the electronic configuration
What shell of the atom has the most energy
The outer shell has the most energy as the further away from the nucleus the more energy the shell has
What are the noble gases
They are unreactive all having full outer shells and are thus very stable with the exception of helium still having a full outer shell but only two as the smallest shell only has two compared to eight
What’s a compound
A pure substance made up of two or more elements chemically combined.
Compounds cannot be separated into their elements by an physical means
E.g copper sulphate and calcium carbonate
What is a mixture
A combination of two or more substances (elements and/or compounds) that are not chemically combined
Mixtures can be separated by physical methods such as filtration or evaporation.
E.g sand and water
What are metalloids/semimetals
Most elements are metals and a small number of elements display properties of both metal and acid. These elements are called metalloids or semimetals
What are the properties of metal
Conduct heat and electricity
Are malleable and ductile (can be hammered and pulled into different shapes)
Tend to be lustrous (shiny)
Have high density and usually have high melting points
Form positive ions through electron loss
Form basic/base oxides
What are the properties of non metals
Do not conduct heat and electricity
Are brittle and delicate when solid and easily break up
Tend to be dull and nonreflective
Have low density and low melting points (many are gases at room temperature)
Form negative ions through electron gain (except for hydrogen)
Form acidic oxides
What are alloys
Alloys are mixtures of metals, where the metals are mixed together but are not chemically combined. Though they can also be mixed with non metals such as carbon.
Why are alloys mostly harder than normal metals
Alloys contain atoms of different sizes, which distorts the regular arrangements of atoms
This makes it more difficult for the layers to slide over each other, so they are usually much harder than the pure metal
What is an ion
An ion is an electrically charged atom or group of atoms formed by the loss or gain of electrons
What holds ionic compounds together
The positive and negative charges are held together by the strong electrostatic forces of attraction between opposite forces.
This is what holds ionic compounds together
What is a lattice structure
Lattice structure refers to the arrangement of the atoms of a substance in 3D space
In lattice structures, the atoms are arranged in an ordered and repeating fashion
The lattices formed by ionic compounds consist of a regular arrangement of alternating positive and negative ions
E.g diamond
What are covalent bonds
compounds that are formed when electrons are shared between atoms
Only non-metal elements participate in covalent bonding
What are the properties of ionic compound
Have high melting and boiling points so ionic compounds are usually solid at room temperature
Not volatile so they don’t evaporate easily
Usually water-soluble as both ionic compounds and water are polar
Conduct electricity in molten state or in solution as they have ions that can move and carry a charge
What are the properties of covalent compounds
Have low melting and boiling points so covalent compounds are usually liquids or gases at room temperature
Usually volatile which is why many covalent organic compounds have distinct aromas
Usually not water-soluble as covalent compounds tend to be nonpolar but can dissolve in organic solvents
Cannot conduct electricity as all electrons are involved in bonding so there are no free electrons or ions to carry the charge
What is non polar and polar
Polar refers to the distribution of electrons in an atom not sharing electrons that’s why covalent bonding is non polar whale ionic bonding is polar
Melting points and Boiling points of covalent and ionic compounds
Covalent compounds have weaker intermolecular bonds. It is these weak intermolecular forces that break, not the strong covalent bonds
Less energy is needed to break the molecules apart, so they have lower m.p. and b.p. than ionic compounds
What are allotropes
Different atomic or molecular arrangements of the same element in the same physical state.
E.g diamond and graphite are allotropes of carbon which are giant covalent structures
What are giant covalent structures
This class of substances contains a lot of non-metal atoms, each joined to adjacent atoms by covalent bonds forming a giant lattice structure. Giant covalent structures have high melting and boiling points because of their strong covalent bonds. Large amounts of heat energy are needed to overcome these forces and break down bonds
What are the uses of giant covalent structures
Diamond is used for jewellery as it does noir conduct electricity is the hardest substance in the world and one off the best looking in the world.
Graphite can conduct electricity so Graphite is used in pencils and as an industrial lubricant, in engines and in locks
It is also used to make non-reactive electrodes for electrolysis as it’s conductive
What has intermolecular bonds got to do with conductivity
If structures have got weaker intermolecular bounds it’s known that they conduct electricity more as the electrons within them move more freely then when the intermolecular bonds are strong.
What happens in a metal lattice
Within the metal lattice, atoms lose their valence electrons and become positively charged
The valence electrons no longer belong to any metal atom and are said to be delocalised
They move freely between the positive metal ions like a sea of electrons
Why are metallic bonds strong
Metallic bonds are strong and are a result of the attraction between the positive metal ions and the negatively charged delocalised electrons
What does malleable and ductile mean
They are layers of positive ions that can slide over one another and take up different positions
Metallic bonding is not disrupted as the valence electrons do not belong to any particular metal atom so the delocalised electrons will move with them.
They can be hammered and bent into different shapes without breaking
