atoms

What are the three ideas in John Dalton's theory about the atom?

Atoms cannot be created, divided or destroyed. Atoms of the same element are exactly the same and atoms of different elements are different. Atoms join with other atoms to make new substances.

What discovery caused the original Dalton model of an atom to change?

The discovery of subatomic particles.

How did JJ Thomson discover the electron?

Thomson experimented with a cathode ray tube. The beam moved towards the positively charged plate, indicating that the particles must have a negative charge.

What is the atomic model proposed by JJ Thomson?

Plum pudding model: Negatively charged electrons scattered through a positively charged material.

What did Ernest Rutherford discover from his gold foil experiment?

Most particles passed straight through suggesting that atoms were mostly empty space. A few were deflected and some bounced back, indicating a tiny, dense, positively-charged nucleus.

Describe Rutherford's new model of the atom.

Mass is concentrated in the central nucleus. Mostly empty space. Electrons travel in random paths around the nucleus.

Describe the structure of an atom.

Small central nucleus made up of protons and neutrons. Electrons orbit the nucleus in shells.

What is the radius of the nucleus compared to the atomic radius?

The radius of the nucleus is 1x10^-14 m, which is 1/10000 of the atomic radius.

What are the relative masses of protons, neutrons, and electrons?

Proton: 1, Neutron: 1, Electron: 1/1836.

What are the relative charges of protons, neutrons, and electrons?

Proton: +1, Neutron: 0, Electron: -1.

Why do atoms contain equal numbers of protons and electrons?

Atoms are stable with no overall charge. Protons are positively charged and electrons are negatively charged, so their numbers must be equal for balance.

Where is the mass of an atom concentrated?

In the nucleus.

What does the atomic number of an atom represent?

The number of protons.

What does the mass number of an atom mean?

The mass number is the number of protons and neutrons found in the nucleus of an atom.

Fill in the blank: 'Atoms of the same element have the same number of ______ in the nucleus and this is unique to that element.'

Protons.

What is an isotope?

Isotopes are atoms with the same number of protons but a different number of neutrons. Isotopes of an element have the same atomic number but different mass numbers.

How many protons, electrons, and neutrons does Boron have?

5 protons, 5 electrons, 6 neutrons.

Why is the relative atomic mass not always a whole number?

Different isotopes of the same element have different mass numbers. The relative atomic mass is an average of the masses of all these isotopes.

What two values are required to calculate the relative atomic mass of chlorine?

Mass numbers and relative abundances of all the isotopes of chlorine.

How did Mendeleev arrange the elements in his periodic table?

Elements arranged with increasing atomic masses. Elements with similar properties were put into groups.

How was Mendeleev able to predict the properties of new elements?

He left gaps in his periodic table and used the properties of elements next to these gaps to predict the properties of undiscovered elements.

Why did Mendeleev's table lack some accuracy?

Isotopes were poorly understood at the time, and protons and neutrons had not yet been discovered.

How are elements arranged in the modern periodic table?

In order of increasing atomic number.

Fill in the blank: 'Elements in the same group (column) have similar _______ ______.'

Chemical properties.

Why do elements in the same column have similar chemical properties?

They have the same number of outer shell electrons.

What does the period (row) number tell you about all the elements in that period?

Elements in the same period have the same number of electron shells.

What does the group (column) number tell you about all the elements in that group?

All elements in the same group have the same number of outer electrons.

On which side of the periodic table are the metals positioned?

Left hand side.

What determines whether an element is a metal or non-metal?

Atomic structures of the elements.

What is the maximum number of electrons allowed in each of the first 3 shells?

2 in the first shell, 8 in the second shell, and 18 in the third shell.

What is the maximum number of electrons allowed in the 1st shell?

2

What is the maximum number of electrons allowed in the 2nd shell?

8

What is the maximum number of electrons allowed in the 3rd shell?

8

When are atoms most stable?

When they have full electron shells.

What is the atomic number of sodium (Na)?

11

What is the electron configuration of sodium (Na)?

2, 8, 1

How is the electron configuration of an element related to its position in the periodic table?

The number of rings indicates the period, and the number of electrons in the outer ring indicates the group.

What is an ionic bond?

A bond between a metal and non-metal involving the transfer of electrons.

What happens to the metal atom during ionic bond formation?

The metal atom loses electrons to become a positively charged ion (cation).

What happens to the non-metal atom during ionic bond formation?

The non-metal gains electrons to become a negatively charged ion (anion).

What is an ion?

An ion is an atom or group of atoms with a positive or negative charge.

If an ion is positively charged, has it lost or gained electrons?

It has lost electrons.

How many protons, neutrons, and electrons are in Na+?

Protons: 11, Electrons: 10, Neutrons: 12.

How many protons, neutrons, and electrons are in O2-?

Protons: 8, Electrons: 10, Neutrons: 8.

Why do elements in groups 1, 2, 6, and 7 readily form ions?

To become more stable and achieve the electron structure of noble gases (group 8).

What type of ions do elements in group 1 form?

Cations (positive), specifically 1+ ions.

What type of ions do elements in group 2 form?

Cations (positive), specifically 2+ ions.

What type of ions do elements in group 6 form?

Anions (negative), specifically 2- ions.

What type of ions do elements in group 7 form?

Anions (negative), specifically 1- ions.

What does it mean if an ionic compound ends in -ide?

The compound contains 2 elements.

What does it mean if an ionic compound ends in -ate?

The compound contains at least three elements, one of which is oxygen.

Describe the structure of an ionic compound.

Lattice structure with a regular arrangement of ions held together by strong electrostatic forces.

What is the chemical formula of sodium oxide formed from Na+ and O2-?

Na2O.

What is the chemical formula of magnesium hydroxide formed from Mg2+ and OH-?

Mg(OH)2.

What is a covalent bond?

A bond formed when an electron pair is shared between two atoms.

What forms as a result of covalent bonding?

A molecule.

True or false? 'Covalent bonds are weak.'

FALSE.

Which is smaller, an atom or a molecule?

An atom.

Why do ionic compounds have high melting points?

Strong electrostatic attraction between positive and negative ions requires a lot of energy to overcome.

When do ionic compounds conduct electricity?

When molten or aqueous because the ions are charged and free to move.

Why do simple molecular compounds have low melting and boiling points?

They have weak intermolecular forces which require little energy to overcome.

Do simple molecular compounds conduct electricity? Why or why not?

No, because there are no charged particles.

Do giant covalent structures have a high melting point?

Yes, because they have many strong covalent bonds that require a lot of energy to break.

How do metals conduct electricity and heat?

The positive ions are fixed in a sea of delocalised electrons that are free to move.

True or false? 'Metals are insoluble in water.'

TRUE.

Name two giant covalent structures formed from carbon atoms.

Graphite and Diamond.

Describe the structure of graphite.

Each carbon atom is bonded to 3 other carbon atoms in layers of hexagonal rings.

Describe and explain the properties of graphite.

Graphite is soft/slippery due to weak intermolecular forces between layers and conducts electricity because of delocalised electrons.

Describe the structure of diamond.

All carbon atoms are covalently bonded to four other carbon atoms with no delocalised electrons.

What are the properties of diamond?

Very hard, very high melting point, doesn't conduct electricity.

What are the uses of graphite?

Electrodes (conducts electricity, high melting point), lubricant (slippery layers).

Why is diamond used in cutting tools?

It is very hard.

What is a fullerene?

A molecule made of carbon, shaped like a closed tube or hollow ball.

Name two fullerenes.

Graphene, C60 (buckminsterfullerene).

What are the properties of the fullerene C60?

Slippery, low melting point, spherical, strong covalent bonds, large surface area.

What are the properties of graphene?

High melting point, conducts electricity due to delocalised electrons.

Why is graphene useful in electronics?

Extremely strong, has delocalised electrons that can carry charge, only one atom thick.

What is a polymer?

Long chain molecules formed from many monomers.

Name a polymer.

Poly(ethene).

What bond is formed between carbon atoms in polymer molecules?

Covalent bonds.

What are the properties of metals?

High melting point, high density, good conductors of electricity, malleable, ductile, generally shiny.

Why are metals malleable?

Atoms are arranged in uniform rows that can slide over one another.

Why can metals conduct electricity?

Electrons in the metal are charges that can move.

What are the general properties of non-metals?

Low boiling points, poor conductors of electricity, brittle when solid.

What are the limitations of dot and cross models for ionic compounds?

No lattice structure or ionic bonds.

What are the limitations of 2D diagrams for ionic compounds?

Only shows one layer, doesn't show formation of ions.

What are the limitations of 3D diagrams for ionic compounds?

Shows spaces between ions, doesn't show charges.

What are the limitations of dot and cross models for covalent molecules?

Doesn't show relative sizes of atoms or intermolecular forces.

What are the limitations of ball and stick models for covalent molecules?

Bonds shown as sticks rather than forces, doesn't show how covalent bonds form.

How do you calculate the relative formula mass of a compound?

Add together all the relative atomic masses of the atoms in the compound.

What is the empirical formula?

The smallest whole number ratio of the atoms of each element in a compound.

What values can be used to calculate the empirical formula?

Reacting masses or percentage composition.

What is the empirical formula for Fe2O4?

FeO2.

What is the molecular formula?

Actual number of atoms of each element in a compound.

Describe an experiment to work out the empirical formula of magnesium oxide.

Weigh magnesium, heat in a crucible, weigh magnesium oxide, calculate mass of oxygen, calculate moles, find ratio.

What is the law of conservation of mass?

No matter is lost or gained during a chemical reaction.

What happens to mass in a closed system during a reaction?

Mass stays constant.

What happens to mass in an open flask when a gas is produced?

Mass decreases as the gas escapes.

Using the law of conservation of mass, what mass of oxygen is needed if 52g of calcium reacts with oxygen to form 79g of calcium oxide?

27g of oxygen.

What equation links mass, moles, and relative atomic mass?

Mass (g) = Moles x Relative atomic mass (Mr).