Everything Chem !!

define gravimetric analysis

the mass of each substance present in a given quantity of the mixture, or to know the percentage composition of the mixture.

What elements listed are gaseous non-metals at room temp?

noble gases

can non-metals conduct electricity? why or why not?

no, because the electrons present inside the metal can not freely move around

can metals conduct electricity? why or why not?

yes, because the electrons present inside the metal are free to move in any direction.

define chemical changes

• a change in the physical and chemical properties

• a new substance is formed

define physical changes

• a change in size, shape or state

• no new substance is formed

define chemical property

• indicates how a substance reacts with something else

• matter will be changed into a new substance after the reaction

define physical property

• observed with sense

• determined without destroying matter

charge of neutron

1 n

0

charge of proton

1 H

1

half life

average time it takes for the number of radioactive nuclei in the sample to halve

relative formula mass

the sum of the relative atomic masses of the atomic species as given in the stated formula of the compound.

what is relative atomic mass?

average mass of the atoms in the naturally occurring element

why are atoms electrically neutral?

Atoms are electrically neutral because they have equal numbers of protons (positively charged) and electrons (negatively charged). This also means the overall charge on the atom is zero. If an atom gains or loses one or more electrons, it becomes an ion.

Neutrons

Neutral subatomic particles found in the nucleus of an atom, with a relative mass of 1.

What is unstable nuclei?

unstable atoms which have too many or too few of neutrons.

How does unstable nuclei become stable?

undergo radioactive decay where particles or energy is emitted

what is the beta particle

electron emitted from the nucleus. the neutron then decays into a proton

what is the gamma ray particle

- not a particle but high energy electromagnetic radiation
- cancerous
- high frequency, small wavelength

Define penetration

ability to travel through materials

define range

how far radiation can travel through the air

what happens to an atom when it is ionised?

it has gained or lost one or more electrons

Define ionising ability

when radiation forms ions

define isotopes

atoms with the same number of protons but different number of neutrons

describe the bohr model

-electrons circling around nucleus in orbits
-each orbit has a specific energy level
-orbits closer to nucleus = lower energy
-lots of empty space between nucleus and electron

define hund's law

every orbital must be filled with one electron of the same spin, before being filled with a second electron
- fill every orbital first before moving on

define the pauli exclusion principle

no more than 2 electrons can occupy a single orbital, and paired electrons must be of the opposite spin

define the aufbau principle

lower energy levels must be occupied first before occuping higher energy levels

Atomic Number

The number of protons and electrons in the nucleus of an atom, denoted by the symbol 'z'.

Mass Number

The total number of protons and neutrons in the nucleus of an atom, denoted by the symbol 'A'.

Protons

Positively charged subatomic particles found in the nucleus of an atom, with a relative mass of 1.

Electrons

Negatively charged subatomic particles found orbiting the nucleus of an atom, with negligible mass in the context of the mass number.

Do protons have a positive or negative charge?

positive charge

Do electrons have a positive or negative charge?

negative charge

How do you find the amount of neutrons

mass number - protons

What is in the centre of the atom?

nucleus

What is the nucleus composed of?

protons and neutrons

Do neutrons have a positive or negative charge?

no charge

What does the number of electrons in the outer shell determine?

determines which group the element belongs to on the periodic table

What is the law of constant composition?

a compound always has the same elements in the same proportions by mass

eg. water (H2O) will always be composed of two hydrogen atoms and one oxygen atom, in a fixed ratio of hydrogen to oxygen. (1:8)

what is the alpha particle?

big particle (2 protons, 2 neutrons), helium nucleus

provide details on the alpha particle

- short range due to its size, can only travel a few centimeters in the air
- least penetrating, moderate
- blocked by a sheet of paper
- charge of particle: +2

provide details on the beta particle

- smaller than alpha, lower energy than the gamma ray
- higher range than alpha particle, can travel a few meters of air
- moderate penetration, passes through a sheet of paper, 0.5mm of aluminum but not 0.5mm of lead
- charge of particle: -1
- moderately ionising

provide details on the gamma ray particle

- no mass
-short wavelength, carries large amounts
- large range: travels kms through the air or indefinitely in space
- highly penetrating: only meters of concrete can stop it
- weakly ionising due to no mass

define radioactivity

the spontaneous emission of radiation or particles that occurs with certain isotopes and arises because some isotopes are unstable. also due to the spontaneous disintegration of atomic nuclei.

is nuclei radioactive?

yes

is stable nuclei radioactive?

no

Name the positives of Bohr's Model

- states that electrons exist in energy levels
- increasing energy levels hold greater amounts of electrons
- explains emission of unique colours released by small atoms
- predicts the behaviour of electrons around the nucleus
- simple and intuitive model

Name the negatives of Bohr's model

- limited to hydrogen-like atoms (with one electron)
- did not explain that electrons moving in a circular motion should emit electromagnetic radiation and lose energy
- impossible to know exact position and velocity (speed) of particles

Heinsberg uncertainty principle

states that it is impossible to measure or calculate simultaneously both the position and momentum (speed) of an electron or any other particle

Describe Schrodinger's model

- uses quantum mechanisms to predict the most probable location of electrons
- electrons can not be in defined rings but we can calculated where they are found
- energy levels (approved), defined orbits (disproved)
- each energy level has subshells which contains orbitals

Name the positives of Schrodinger's Model

- accurate predictions on the behaviour of particles
- speaks on how electrons are waves
- can be applied to multi-electron atoms and molecules rather than just hydrogen like atoms
- foundation for quantum phenomena

Octet Rule

every atom wants to have eight valence electrons in its outermost electron shell.

define covalent compounds

sharing of electrons between 2 nonmetals

define ionic compounds

transfer of electrons between metals and non-metals

define cations

positively charged ions (loses electrons)

define anions

negatively charged ions (gain electrons)