Tom chemistry

from chemisty lessons so be smart

What is an atom?

An atom is the smallest part of an element that can exist and still retain the properties of that element.

What is an element?

A substance made up of only one type of atom.

What is an ion?

An atom or group of atoms with an overall electrical charge because it has gained or lost electrons.

What is an isotope?

Atoms of the same element with the same number of protons but different numbers of neutrons.

What is the atomic number?

The number of protons in the nucleus of an atom.

What is the mass number?

The total number of protons and neutrons in the nucleus.

How do you calculate the number of neutrons?

Mass number − atomic number.

What is a positive ion (cation)?

An ion formed when an atom loses one or more electrons, giving it an overall positive charge.

What is a negative ion (anion)?

An ion formed when an atom gains one or more electrons, giving it an overall negative charge.

Why do atoms form ions?

To obtain a more stable electron arrangement, usually a full outer electron shell.

What happens to electrons when an ionic bond forms?

Electrons are transferred from a metal atom to a non-metal atom.

What happens to a metal atom when it forms an ion?

It loses electrons and becomes a positively charged ion.

What happens to a non-metal atom when it forms an ion?

It gains electrons and becomes a negatively charged ion.

Why is a metal ion positive?

It has fewer electrons than protons.

Why is a non-metal ion negative?

It has more electrons than protons.

What is an ionic bond?

The strong electrostatic force of attraction between oppositely charged ions.

What type of elements usually form ionic compounds?

Metals and non-metals.

What is an ionic compound?

A compound made from positively and negatively charged ions held together by ionic bonds.

Why do oppositely charged ions attract?

Opposite electrical charges exert an electrostatic force of attraction on each other.

Why do ionic compounds have high melting and boiling points?

There are strong electrostatic forces of attraction between oppositely charged ions, which require lots of energy to overcome.

What is covalent bonding?

The strong electrostatic attraction between a shared pair of electrons and the nuclei of the bonded atoms.

What type of elements usually form covalent bonds?

Non-metal atoms.

What happens to electrons in a covalent bond?

They are shared between atoms.

What is a single covalent bond?

One shared pair of electrons.

What is a double covalent bond?

Two shared pairs of electrons.

What is a triple covalent bond?

Three shared pairs of electrons.

How many electrons are represented in a single covalent bond?

Two electrons: one from each atom.

How are covalent dot-and-cross diagrams drawn?

Draw overlapping outer electron shells and place shared electron pairs in the overlap, using dots and crosses to show which atom the electrons came from.

What is metallic bonding?

The strong electrostatic attraction between positive metal ions and delocalised electrons.

What are delocalised electrons?

Electrons that are free to move throughout the structure rather than being attached to one particular atom.

What particles are found in a metal's structure?

Positive metal ions surrounded by a sea of delocalised electrons.

Why do metals conduct electricity?

Their delocalised electrons can move through the structure and carry electrical charge.

What is nanoscience?

The study of very small particles and structures, generally between 1 and 100 nanometres in size.

What is a nanoparticle?

A particle with a size between approximately 1 and 100 nanometres.

How small is a nanometre?

One nanometre is 1 × 10⁻⁹ metres.

How does surface area to volume ratio change as particle size decreases?

As particle size decreases, the surface area to volume ratio increases.

Why can nanoparticles be more reactive than larger particles of the same material?

They have a much higher surface area to volume ratio, so a greater proportion of their atoms are exposed at the surface.

Why can nanoparticles be useful as catalysts?

Their high surface area to volume ratio provides more surface for reactions to take place.

Give an example of a use of nanoparticles.

Nanoparticles can be used in catalysts, medicine, cosmetics, sunscreens and electronic materials.

What are two possible concerns about nanomaterials?

Their effects on human health and the environment may not be fully understood.

Why is more research needed into nanomaterials?

Because their small size and increased reactivity may cause effects that are not yet fully understood.