Chem Unit test

Investigating Matter

Matter: anything with mass and volume

Mass: amount of matter in a substance, measured in grams(g)

Volume: amount of space a substance occupies, measured in litres(L)

Density: Density compares the mass of a substance to its volume

• mass/volume = g/mL or g/cm³

Changes in Matter

A) Chemical → New Matter

B) Physical → No new matter

A) Chemical Change

• A chemical change is a change in matter when substances combine(or separate) to form new substances

• These new substances have new properties

• Things to look for: bubbles form, precipitate(a solid forms after mixing 2 liquids), colour change, smell and sound

B) Physical Change

• A physical change is a change in matter when no new substance is formed

• The substance may have a different appearance but its properties stay the same

• This is because no chemical bonds are formed or destroyed in a physical change

• Changes of state between solid, liquid, and gas do not produce new substances and are physical changes

The Kinetic Molecular Theory

Kinetic energy

• The energy of motion

• All particles are moving and have kinetic energy

• The more energy the particles have, the faster they move and the farther apart they get

The Kinetic Molecular Theory states:

• All matter is made up of tiny particles

• Different substances have different particles

• The particles are in constant motion

• energy makes particles move

  • Solid: particles are close together and can only vibrate

  • Liquid: particles are further apart and slide by each other

  • Gas: particles are very far apart and move quickly

The Kinetic Molecular Theory and Changes of State

Changes of state: changing from one state to another

• A change of state happens when energy(heat) is added or removed

• Solids have the least amount of energy

• Gasses have the most amount of energy

• gas→liquid = condensation

• liquid → gas = evaporation

• liquid → solid = solidification

• solid → liquid = melting

• solid → gas = sublimation

• gas → solid = deposition

Temperature and Changes of State

• Boiling point: temperature to change from liquid to gas

• Condensing point: temperature to change from gas to liquid

• Melting point: temperature that changes solid to liquid

• Freezing point: temperature that changes liquid to solid

Describing Matter

• a) Physical properties (characteristics that can be observed or measured without changing its chemical identity of matter) of matter can be classified as:

  • qualitative properties: descriptions that are not measured with a number(quality)

  • quantitative properties: descriptions that are measured with a number(quantity)

• b) Chemical properties: describe the ability of matter to react with another substance to form different substances

  • examples: combustibility, lack of reactivity, reactivity with oxygen, etc.

Classification of Matter

All substances can be classified as: i) pure substances or ii) mixtures

• i) Pure substance: substance that is made up of one type of particle; cannot be separated by physical means

  • a) elements - made up of one type of atom; cannot be broken down further

    • eg. Oxygen(O), Hydrogen(H)

  • b) Compounds - substance made up of two or more different kinds of elements that are held together by chemical bonds; can be broken down into simpler substances

    • eg. Water(H2O), Salt(NaCl)

• ii) Mixture: contains two or more pure substances; can be separated by physical means

  • eg. salt water

  • a) Homogeneous mixtures (solutions): mixed uniformly; cannot see their components

    • example: air(nitrogen, oxygen, hydrogen), steel(iron and other elements)

  • b) Heterogeneous mixture: have different components that you can see

    • ex. beach sand, salad dressing

The Atomic Theory

The Atomic Theory: All matter is made up of atoms, which are particles too small to be seen.

• The atom: smallest unit of an element that has the properties of that element

Inside the Atom

• Each element is classified by its own kind of atom

• Each atom is made up of three subatomic particles:

  • proton

  • neutron

  • electron

Most of the mass of the atom is in the nucleus.

Elements

Elements are the building blocks of matter.

Chemical Symbols

• Chemical symbol: symbolic system to describe all elements using letters from their Greek or Latin name

• To give every element a unique symbol:

  • Every element is represented by the first letter of its name or by the first two letters of its name

  • When the first letter was previously used, a letter from the rest of the name is added

    • eg. C = carbon so Ca = calcium, Co = cobalt, Cr = chromium

• The first letter is always capitalized and the second is lower case

Describing Elements

We can describe elements by:

• physical properties: the appearance of a substance (eg. colour)

• chemical properties: substance’s ability to chemically react with other substances to form new products

Elements are classified as a) metals, b) non-metals, c) semi-metals/metalloids

A) Metals:

• most elements are metals

• metals have the following properties:

B) Non-metals:

• non-metals have the following properties:

C) Semi-metals/Metalloids

• elements that share some properties with metals and some properties of non-metals

The Periodic Table and Chemical Properties

Mendeleev’s Table

Elements are organized based upon some important methods first introduced by Dmitiri Mendeleev:

1. Arranged elements by increasing atomic mass

2. Grouped elements into “families” based on similar properties(density, melting point)

3. Made the assumption that some elements were still undiscovered and left areas of the table blank

Modern periodic table is ordered by increasing atomic number

The Periodic Table

A chart that organizes elements according to their chemical and physical properties.

Each box in the periodic table gives the element’s:

• name

• symbol

• atomic number

• atomic mass

• common ion charge(s)

Atomic number:

• number of protons in an atom’s nucleus

• identifies the element

pattern: atomic number increases by 1 across rows

Atomic mass:

• average mass of all atoms of one element

• measured in atomic mass units(amu)

pattern: atomic mass tends to increase along with the atomic number

Ion charge:

• electric charge of the ion (atom gains/loses electrons)

• negative charge = gained electrons

• positive charge = lost electrons

• if more than one charge is written = that an atom can gain/lose a different number of electrons

pattern:

• elements on the left(metals) tend to have positive ions

• elements on the right(non-metals) tend to have negative ions

• elements in the same chemical family form ions with the same charge

Table Arrangement: Periods and Families

The modern periodic table organizes elements in groups and periods.

Period:

• horizontal row

• numbered 1 to 7

Chemical family:

• vertical row called a group

• elements in a group have similar physical and chemical properties

• numbered 1 to 18

Elements of Groups 1, 2, 3 and 13 to 18 are called main-group elements or representative elements

Elements in Groups 3 to 12 are called transitional elements

Four well-known elemental families

Alkali metals(group 1):

• Li, Na, K, Rb, Cs, Fr (NOT H)

• highly reactive(reactivity increases down the group)

• react with water and oxygen

• low melting point

• very soft

Alkaline earth metals(group 2):

• Be, Mg, Ca, Sr, Ba, Ra

• less reactive than Group 1

• burns in air if heated and produces bright flames

• reacts with water(not as violent as Group 1)

Halogens(group 17):

• F, Cl, Br, I, At

• non-metals

• highly reactive

Noble Gases(Group 18):

• He, Ne, Ar, Kr, Xe, Rn

• Non-metals

• most stable and unreactive of all elements

The Periodic Table and Atomic Theory

• patterns in the periodic table occur as a result of regular changes in the structure of the atoms of elements

• elements line up in columns because they are similar in the arrangement of their electrons

• Niels Bohr:

  • suggested that electrons move around the nucleus of an atom in orbits or shells

• Bohr model:

  • a diagram that shows how many electrons are in each shell surrounding the nucleus of an atom

• electron shells:

  • regions surrounding the nucleus of an atom

  • each shell is a certain distance from the nucleus

Each shell holds a different number of electrons

Bohr model diagrams

How to draw a Bohr Model Diagram:

1. Write the element symbol

2. Check the periodic table to see how many electrons the element has (in a neutral atom: #protons = #electrons)

3. paying attention to how many electrons each shell can hold, figure out how many shells the atom has

4. draw a circle around the element symbol for each shell

5. use a dot to represent an electron. Starting with the inner shell, put the correct number of electrons on the diagram

Valence electrons and Chemical Families

• Valence = outer

• Valence electrons: electrons in the outermost shell

• Valence shell: highest occupied energy level

important patterns:

• elements in the same family/group have the same number of valence electrons

• elements in the same period have valence electrons in the same shell

• period number indicated the number of shells that contain electrons

Noble Gas Stability

• when a valence shell is full, the atom is stable

• noble gas atoms(group 18) have filled valence shells, which makes them virtually unreactive

• atoms in other groups need to gain or lose electrons to become stable(full valence shell) during a chemical reaction

How Atoms Become Ions

Ion: atom that has gained or lost electrons, and as a result has a charge

Positive Ion:

• if an atom loses electrons(loses negative charges), then the atom becomes positively charged

• since atoms of metals have 1, 2, or 3 valence electrons, they want to lose their valence electrons to become positive ions

Negative Ion:

• if an atom gains electrons(gains negative charges), then the atom becomes negatively charged

• since atoms of non-metals have more than 3 valence electrons, they want to gain valence electrons to become negative ions

Reactivity

1) Reactivity of an element is linked to how close it is to having a full valence shell

• most reactive elements: groups 1 and 17(elements are only one electron away from a full valence shell)

• example: Sodium(group 1) easily gives up an electron, since it exposes the full valence shell underneath

2) Reactivity increases as you move down the family

• example: group 1 metals: potassium is more reactive than sodium

Atomic Size Trends

1) Atomic size increases moving down a group

• As you move down a group, elements have atoms with increasing numbers of energy shells

• The greater the number of shells, the farther the valence electrons are from the nucleus, and the larger the atom

2) Atomic size decreases moving left to right across a period

• elements have increasing numbers of electrons across a period

• number of occupied valence shells stay the same, but the number of protons in the nucleus increases

• attraction between valence electrons and the nucleus increases because a greater positive charge on the nucleus pulls more strongly on the electrons

• therefore, the electrons are pulled more tightly towards the nucleus, leading the decreasing atomic size

Compounds

Compounds account for the huge variety of matter on Earth

Compound: a pure substance made up of 2 or more different kinds of elements that are held togther by chemical bonds