An atom is a building block of all matter (all things that are solid/liquid/gas). An atom the smallest single building block that makes up all mater. An atom is made of: protons, neutrons and electrons.
An element is 2 or more of the same atom.
E.g. – O3.
The periodic table of elements is a list of 118 elements known to science.
Atomic No: The number of protons in the nucleus.
The first letter is always uppercase. The second/third letter is always lowercase.
An atom is a single. An element is made of multiple atoms that are the same. A compound is made of multiple atoms that are different.
A compound is a special molecule that has 2 or more different atoms in a ratio.
E.g. – HNO3, CO2.
2 or more atoms in a special ratio.
E.g. – H2O.
An ion is a charged atom that has lost or gained an electron. Cation = lost electron. Anion = gained electron.
A cation is a positive ion it has LOST electrons.
Na+ – Sodium ion has lost 1 electron. Cation is a positive ion.
Mg2+ – Magnesium ion lost 2 electrons. 12+ 10-.
Li+ – Lithium ion 1 electron. 3+ 2-.
Ca2+ – Calcium lost 2 electron. 20+ 18-.
An anion is a negative ion it has GAINED electrons.
Cl– – Chlorine has gained 1 electrons. 17+ 18-.
Br– – Bromine has gained 1 electrons. 35+ 36-.
O2– – Oxygen has gained 2 electrons. 8+ 10-.
An isotope is an atom that has the same of the number of protons but different number of neutrons.
Atomic No: the number of PROTONS in the nucleus of an atom.
Mass No: the number of PROTONS + NEUTRONS in the nucleus of an atom.
A lens is a transparent piece of plastic or glass that is shaped to curve inwards or outwards. A lens refracts light.
There are two types of lenses: Convex and Concave
A convex lens bends light in, converges light to a point called the focal point. A convex lens is also called a converging lens.
A diverging lens spreads light out, diverges light out.
(light dies in a cave concave = diverging)
Light is a form of energy called electromagnetic radiation. Light travels as waves, e.g. UV rays, X-rays, infrared light, and microwaves. Light is the fastest thing in the universe. Light travels at a speed of 300,000 km per seconds.
Transparent: allowing light to pass through so that objects behind can be distinctly seen
Translucent: allowing light to pass through but not detailed shapes, to pass through
Opaque: not allowing light to pass through
Radiation transmits heat as invisible waves that travels at the speed of light (around 300,000 km per second).
Forms of radiation:
Infrared – night vision
Heat is radiated from fires
Radiation for cancer kills cancer cells
Radiation can be:
Absorbed – taken into the object especially black and dark colours
Reflected – the heat energy bounces off as waves
Transmitted – transmit means ‘travels through’. The waves pass through glass
Regular reflection is when an image is seen in a flat surface. The light rays are reflected back.
Diffuse reflection is when no image is seen in a rough surface because the light is reflected back at all angles.
Refraction is the bending of the light. Refraction occur when it passes from a medium with a different density.
Solubility is how easily an ionic compound dissolves.
What is sound?
Sound is produced when something vibrates. E.g. speech – flaps of skin vibrate, and drum – strings inside the piano vibrate.
Sound is produced when something vibrates so it makes particles in the air vibrate.
A sound wave is the movement of alternating compressions and rarefactions.
Sound waves rely on particles to vibrate in: sold, liquid and air.
Compression is when vibrations creates regions of space in which the air particles are bunched together.
Rarefaction is when air particles are more spread out.
Radiation: is a form of heat transfer by invisible waves. Radiation does not transfer from particle to particle, instead it travels through vacuum.
St. Rosemary Educational Institution. "Grade 7 and 8 Science Definitions." http://schoolworkhelper.net/. St. Rosemary Educational Institution, Last Update: 2017. Web. Retrieved on: Monday 27th February 2017. http://schoolworkhelper.net/grade-7-and-8-science-definitions/.