2-Atoms, elements and compounds

2.1 Elements, compounds and mixture 2.2 Atomic structure and the Periodic Table 2.3 Isotopes

What is an atom?

It’s the building block of an element

What’s an element?

• It’s a substance that cannot be further divided into a simpler substance by chemical methods

• All the atoms of an element contain the same number of proton

How many elements are in the periodic

118 known elements

What are the components of the universe?

Hydrogen 92% and helium all other elements contribute to 1% total

What’s a compound?

A substance formed by the chemical combination of 2 or more elements in fixed proportion

What’s a molecule?

Two or more atoms bonded together chemically. They can be the same element or a different elements.

Examples of molecules?

O2 or H2O

Compounds and molecules FACT

All compounds are molecules, but not all molecules are compounds

What is the difference between compounds and molecules

• Molecules focus on the number of atoms bonded (some are different)

• Compounds focus in different elements bonded together

What is the structure of the atom?

• Nucleus with a proton plus a neutron

• Surrounded by electron shells

What is an electron?

A subatomic particle with a negligible mass and a relative charge of -1

Where are electrons located?

They are present in all atoms and are located in the shells (energy levels) outside the nucleus 

What is a proton

A subatomic particle with a relative atomic mass of 1 and a charge of +1 found in the nucleus of all atoms

What is a neutron

• An uncharged subatomic particle present in the nucleus of atoms

• A neutron has a mass of 1 relative to proton

What is a nucleus

• It’s the central region of an atom that’s made up of the protons and neutrons of the atom

• The electrons orbit around the nucleus in different shells/energy levels

What is a subatomic particle?

Very small particles (proton, neutron, electron) from which all atoms are made from

What is the proton/atomic number

It’s the number of protons in the nucleus of an atom

What’s the atomic/nucleon mass?

The number of protons and neutrons in the nucleons of an atom

What are isotopes?

They are atoms of the same element that have the same proton number but different mass/nucleon number (they have a different number of neutrons in their nuclei)

What is the relative atomic mass?

It’s the weighed average mass of the atoms of an element including all isotopes

How do you know the group number 

It’s the total number of valent electrons in the last shell 

How do you know the period number?

The number of energy shells in electron configuration 

What is electronic configuration/structure?

A shorthand method of describing the arrangement of electrons within electron energy levels of an atom

What is a noble gas?

Group 7: monoatomic unreactive gases, they naturally exist as single gases, they don’t make chemical bonds with other atoms

What’s a metal?

It’s a class of chemical elements that all have a characteristic shiny appearance, they are good conductors of heat and electricity 

Where are metals found on the periodic table?

They’re found on the extreme left on the periodic table

What is group 1?

Alkali metals

What is group 2?

Alkali earth metals

What is between group 2 & 3?

Transition metals

What are non-metals?

A class of elements that are typically poor conductors of heat and electricity. 

Where are non-metals found on the periodic table?

They’re found on the right of the periodic table

How does sodium chloride NaCl (salt) form?

If sodium (Na) comes into contact with water, sodium fizzes violently and may even catch a flame

What is unique about NaCl?

It’s a harmless simple salt it’s a compound that bears no direct relationships to the elements that make it

What is a chemical formula?

A short hand method of representing chemical elements and compounds using the symbol of elements

What’s chemical bonding?

A strong force that holds atoms (or ions) in the various structure that chemical substances can form

What are examples of chemical bonding?

metallic bonding, chemical bonding, ionic bonding

What can non-metals do?

• Non-metals gain electrons

• Non-metals form covalent bonding

What is covalent bonding?

Chemical bonding formed by the sharing of one or more pairs of electrons between the atoms

What are simple molecular elements?

Hydrogen molecules H2, Chlorine molecules Cl2, Oxygen molecules O2, Nitrogen molecules N2

What is a dot and cross diagram?

• A diagram drawn to represent the bonding in a molecule or in electrons in an anion. 

• Usually the outer electrons are shown and represented by dot and cross depending on which atoms they are from

What are key points of simple covalent compounds?

• When ever a lone pair is present it pushes the bonds away from it

• Binds arrange themselves in such a way to have minimum repulsion that is at a maximum distance

What are physical properties of simple covalent compounds?

• They have low melting points and boiling points and are often liquid or gases at room temp

• They show poor electrical conductivity

Why do simple covalent molecules have low m.p’s and b.p’s?

Because they are made of simple covalent molecules the intermolecular forces are weak, not much energy is needed to move the forces apart 

Why do simple covalent molecules have poor electrical conductivity?

Because there are no free electrons or ions present to carry the electrical current

What is Ionic bonding?

• Compounds formed between metals and non-metals

• Electrons are transferred from one atom to another, forming ions

• These ionic compounds are held together by ions: electrostatic forces of attraction between oppositely charged ions

What makes things positive and negative?

• Removal of electrons: positive

• Addition of electrons: negative

What does electrolysis mean?

It means electrical current breaking

What’s an anion?

A negative ion attracted to the anode in electrolysis

What’s a cation?

A positive ion that would be attracted to the cathode in electrolysis 

What are important features of ionic bonding?

• Metal atoms always lose their outer electrons to form positive ions (cations)

• The number of + recharges on a metal ion is equal to the # of electrons lost

• The # of negative charges so a non-metal is equal to the # of electrons gained

• In both cases the ions formed have a more stable electronic configuration usually to the nearest noble gas to them in the periodic table

• Ionic bonds result from electrostatic attraction between an oppositely charged ion   

What are physical properties of ionic compounds?

• They have a high mp and bp so they crystalise and are solid at room temp

• They are water soluble because they break into ions

• They only conduct electricity when molten or dissolved in water (not when solid because ions aren’t free to move)

What is a giant ionic lattice?

It’s a lattice held together by the electrostatic forces of attraction between positive and negative ions

What is a feature of ionic crystals?

They are hard but much more brittle than other types of crystal lattice due to the layers in an ionic crystal pushing against each other and bringing ions of the same charge next to each other; the repulsion forces the layers apart

Why can ions in solution conduct electricity?

Because they are able to move so the solution can carry an electric current

Why are ionic crystal lattices called giant structures?

Because the structure itself repeats in all directions

What are giant covalent structures?