All elements have different ways they react together. When elements react they often bond together, make compounds, give out or take in heat or light and change from the elements they were into something new. Where they are in the periodic table can be used to often predict the way they will react as they are in groups based on their similarities.
Elements react together to form compounds. They do this by swapping or moving electrons, a particle in the atom which can be removed and added. When we say chemicals are reactive this is a measure of how easy it is to get them to form compounds with other elements. For example elements like Neon, in the noble gases does not like reacting with other elements and does not want to form compounds. However an element such as sodium is very reactive, when it is placed with other elements it will easily form compounds and react with them, sometimes releasing gases and heat energy.
Flammability is how easy it is for an element to catch fire. We can measure this by heating an object and seeing if it starts burning. Some elements and compounds catch fire very easily and these will burn giving off heat energy. For example oxygen will burn readily when heat is added. But elements such as nitrogen are not very flammable and will not burn easily.
A compound is when two or more elements are joined together by a bond which forms when they share electrons or move them between each other
Elements are atoms with the same number of protons in the nucleus
Flammability is a measure of how easy it is for an element or compound to catch fire