Topic 1.1 - Stoichiometric Relationships Flashcards
(39 cards)
Define an atom
the smallest particle of a chemical element
Define an element
a pure substance containing only one kind of atom, that cannot be broken down into other substances
*elements can exist as an atom (monatomic) e.g. noble gases
*elements can exist as molecules (diatomic)
e.g. oxygen, nitrogen
Define a compound
a chemical combination of two or more different kinds of elements, containing a fixed ratio of atoms.
Define a molecule
a molecule consists of two or more atoms of the same element, or different elements, that are chemically bonded together
- molecules of an element (same atoms)
- molecules of a compound (different atoms)
Define a mixture
two or more different chemical substances that are not chemically combined
what makes up an atom
consists of a nucleus (made up of protons and neutrons), surrounded by electrons
example of a molecule of an element
hydrogen - has 2 hydrogen atoms = H2
oxygen - has 2 oxygen atoms = O2
(known as diatomic molecules)
example of a molecule of a compound
water - 2H + O
table salt - Na + Cl
describe the properties of a compound
the physical and chemical properties of a compound are different from its component elements
example of a mixture
air - made up of chemical compounds such as oxygen, nitrogen, carbon dioxide
*substances burn in air because the oxygen present supports combustion
what changes the properties of compounds compared to their component elements
the bonding between atoms in compounds changes their properties
NaCl - describe the different properties of its component elements
Na + Cl
Na (sodium)
= highly reactive metal that reacts violently with water
Cl (chlorine)
= toxic gas used as a chemical weapon
NaCl (Sodium Chloride)
= white crystalline solid, table salt that we sprinkle on our food
MgO - describe the different properties of its component elements
Mg + O
Mg (magnesium)
= silvery, shiny and hard metal
= burns with bright light and underwater
= conducts electricity and heat
O (oxygen)
= colourless gas
= doesn’t conduct heat or electricity
MgO (magnesium oxide)
= doesn’t conducts electricity in a solid state
= conducts electricity in molten state
= soft white powder
what do the subscripts in a compound convey
the number/ratio of atoms of each element in a compound
what does a chemical equation show
the formation of compounds from elements in a chemical change/reaction
what is the law of conservation of mass
in a chemical reaction, mass is neither created nor destroyed
what are stoichiometric coefficients
the number of units of each term in a chemical equation
what happens to the atoms in a chemical reaction
the number of atoms of each element remains the same
what happens to the properties in a mixture
the properties of the component elements stay the same as they were in pure form
characteristics of mixtures
their composition is not fixed
e.g. air we breathe in contains around 20% of oxygen, whereas the air we breathe out contains around 16% of oxygen
what is a homogenous mixture
uniform composition and properties throughout (looks the same)
what is a heterogenous mixture
non-uniform composition and properties are not the same throughout (you can see differences)
can you separate a mixture
yes, since the components retain their individual properties, they can be separated easily
examples of homogenous substances
table salt, pure gold, brass metal
