Science End of Year Exam

Collision Theory - Define

For a reaction to occur, the particles must collide, they must collide with the appropriate orientation, and they must collide with sufficient energy.

Factors increasing rate of reaction

An increase in: temperature, surface area, concentration and catalysts

How does surface area affect ROR?

Exposes more reactant particles, allowing for more collisions to occur.

How does temperature affect ROR?

An increase in temperature means that particles have more kinetic energy, moving faster, causing more collisions with more energy,

How does concentration affect ROR?

With more reactants, collisions are more likely to occur.

How do catalysts affect ROR?

Catalysts act by creating an alternative reaction pathway, requiring less activation energy in the collision.

Steps in a chemical reaction - List

1. Energy absorbed to break bonds. 2. Particles rearrange into new formation. 3. Energy is released during formation of new bonds.

Exothermic Reactions - Define

Release energy into its surroundings. When the activation energy required to break bonds is less than the energy released when forming bonds.

Endothermic Reactions - Define

Energy is absorbed into the chemical system. When the activation energy required to break bonds is more than the energy released when forming bonds.

Chemical Equation - Exothermic

Reactants -> Products + Energy

Chemical Equation - Endothermic

Reactants + energy -> Products

Energy Conservation - Define

Energy cannot be created or destroyed, so during a chemical reaction energy is absorbed and released.

Aqueous

Dissolved in water.

Activation Energy Symbol

Ea

Enthalpy

The energy contained in a molecule's chemical bonds. Exothermic is negative enthalpy (losing chemical energy), endothermic is positive enthalpy (gaining chemical energy). Symbol: Delta (triangle) H

y-axis of Energy Profile Diagram

Potential energy (or chemical energy/enthalpy)

x-axis of Energy Profile Diagram

Reaction Process

Protons - Define

Positively charged subatomic particles found in the nucleus.

Neutrons - Define

Subatomic particles with no charge found in the nucleus.

Electrons - Define

Negatively charged subatomic particles found in electron shells/orbitals.

Group Number - Define

The amount of valence electrons and in turn similar chemical properties. Columns on the periodic table.

Period Number - Define

The amount of electron shells. Same row.

Atomic Number - Define

The number of protons in the nucleus of an atom.

Atomic Mass - Define

The average mass of all the isotopes of an element relative to the isotope's abundance.

Mass Number - Define

The amount of protons and neutrons in the nucleus of an atom.

Which electron shell has the least energy?

The one closest to the nucleus, as the closer to the nucleus the less energy it holds.

Which electron shell is occupied first?

The closest one to the nucleus, atoms aim to be closer to the nucleus with less energy to maintain stability.

What is the rule for number of electrons in each shell?

2 x n^2, n=energy level. E.g. n=2, 2 x 2^2 = 8

Limitations of the Bohr Model - Describe

1. Cannot predict the emission spectra of atoms with more than one electron, 2. Cannot explain why shells hold 2n^2 electrons, 3. Cannot explain why the 4th shell accepts 2 electrons before the 3rd shell is filled, 4. Atoms are much more complex then Bohr's representation.

Octet Rule - Define

Atoms tend to lose or gain electrons to achieve 8 valence electrons.

What was another name for Schrodinger's model?

Quantum Mechanics

According to Schrodinger what were electrons?

Wave like particles

Orbitals - Define

3D space in which there is a high probability to find an electron.

Explain the different energy levels of Schrodinger's model.

Shells = Major Energy Levels: 1, 2, 3

Subshells = several levels of similar energy: s, p, d, f

Orbitals = Subshells have different orbital amounts: s=1, p=3, d=5, f=7.

Electrons = Each orbital holds at most two electrons: s=2, p=6, d=10, f=14

Isotopes - Define

Atoms with a different number of neutrons. These have similar chemical properties with their similar electron structure; however, they have different physical properties with different mass.

Stable vs Unstable Isotopes

Stable - nucleus unlikely to break apart

Unstable - nucleus is likely to break apart

Radioactive Decay - Define

A spontaneous process in which unstable nuclei lose energy by emitting radiation in the form of particles.

What is the role of neutrons in relation to radio active decay?

Neutrons dilute the repelling forces between protons. Without neutrons the nucleus would break apart as the protons would simply break away from one another. However, too many neutrons would create extra energy in the nucleus and causes the atom to become unbalanced or unstable.

Alpha Decay - Define

Emits an alpha particle: 2 protons, 2 neutrons, from the nucleus, occurring when there are too many nucleons in the nucleus.

Beta Decay - Define

A neutron breaks down into a proton and electron, then the high energy electron is released. Occurs when there are too many neutrons in the nucleus.

Gamma Decay - Define

Releases a photon when there is too much energy within a atom. Usually occurs alongside another form of decay.

Ions - Define

Positively and negatively charged atoms. When an atom begins with a net charge of 0 but loses or gains electrons.

Key Chemical Families - List

Alkali Metals, Alkaline Earth Metals, Transition Metals, Halogens, Noble Gases

Akali Metals - Define

Highly reactive metals which react by losing a singular valence electron.

Alkaline earth metals - Define

Moderately reactive metals which react by losing two valence electrons.

Transition Metals - Define

A wide range of reactivity between groups 3 and 12. Can react by losing an amount of electrons, depending on the metal.

Halogens - Define

Highly reactive non-metals which reacts by gaining a valence electron.

Noble Gases - Define

Low reactivity which tends to be monoatomic (singular atom)

How do ionic compounds form?

Between a metal and a nonmetal, in which the metal gives electrons to the non-metal, usually to achieve a full valence shell or get closer.

Reactivity - Define

How easy it is for electron transfer to occur, depending on the electrostatic forces between atoms.

In accordance to the section of the periodic table, which metals are most reactive?

The bottom left of the periodic table, the metals with the most shells and least valence electrons.

In accordance to the section of the periodic table, which non-metals are most reactive?

The top right of the periodic table, the non-metals with the least shells and most valence electrons.

What is Atomic Radius and its affects of reactivity?

The radius of an atom. A larger atomic radius means that valence electrons are further from the positive electrostatic force of the nucleus, meaning it is easier to lose and harder to gain.

How does atomic radius change on the periodic table?

Increases down a group (more shells) and right to left across a period (lower core charge).

What is Core Charge and its affects of reactivity?

The charge experienced by valence electrons, calculated in: number of protons - number of inner electrons. A larger core charge means that valence electrons experience more attractive forces.

How does chore charge change on the periodic table?

Increases left to right across the periodic table. (More protons while having the same amount of inner electrons)

What is electronegativety and its affects of reactivity?

The ability to attract electrons. Metals have lower electronegativity compared to non-metals, who want to instead attract electrons.

How does electronegativity change on the periodic table?

Increases up (less electron shells, smaller atomic radius) and and left to right across the periodic table (stronger core charge and positive attraction).

What is first ionisation energy and its affects of reactivity?

The energy required to remove an electron in correlation to the positive attraction felt by valence electrons. The more energy required the less likely it is to lose electrons and instead gain electrons.

How does first ionisation energy change on the periodic table?

Increases up (smaller atomic radius and less shells) and left to right across (more core charge so more attraction) the periodic table.

What is metallic Character and its affects of reactivity?

How readily an atom can lose an valence electron. Metals have more metallic character then non-metals, and for metals losing electrons is how they react.

How does metallic character change on the periodic table?

Increases down (increased atomic radius and hence further from nucleus positive charge) and right to left across (smaller core charge so less positive attraction) the periodic table.

Ionic bonding - Define

Occurs between metals and nonmetals as one loses and on gains electrons, meaning that metals become positively charged and non-metals become negative, forming a strong attraction.

Polyatomic Ions - Define

Groups of atoms covalently bonded together.

How to name ionic compounds?

Cation (metal) + Anion (non-metal) + -ide

Cation - Define

Positively charged ion: metal

Anion - Define

Negatively charged ion: Non-metal

Lewis Dot Diagrams vs Bohr Diagrams

Lewis dot diagrams primarily show the valence electrons, ignoring the rest of the subatomic particles, while Bohr is a full representation of the atomic structure.

Bohr vs Schrodinger

Bohr - electrons travel in orbits (fixed circular paths)

Schrodinger - electrons travel in orbitals (3D regions of probability)

Evolution - Define

The change in the characteristics of a species over generations, reliant on the process of natural selection.

Natural Selection - Define

The process in which organisms better suited for their environment tend to survive and produce more offspring, passing down their genetics.

Selective Pressure - Define

An external force which affects an organisms ability to survive or reproduce, thereby causing natural selection.

Variation - Define

The pre-existing differences in individuals organisms within a species.

Speciation and Steps in Speciation - Define

the formation of a new species through divergent evolution.

1. Isolated population

2. Exposure to different selective pressures

3. Distinct traits that create new species that interbreed with one another.

Adaptions - Define

A structure or feature which enables an organism to survive and reproduce within their environment.

Types of adaptions - List, Describe

Physiological: Internal mechanisms, Structural: External Features, Behavioural: The actions and behaviour

Fittest Phenotype - Define

The expressed trait which is best suited to survive an environment.

Steps in Evolution - LIst

1. Variation that exists

2. Selective advantage to certain adaptions

3. Survival of the fittest with a selective pressure

4. Inheritance of advantageous genes

5. Evolve into new species overtime

Charles Darwin's Theory

Spontaneous variation occurred in the individuals of the population and the adaptions best suited for an environment would be passed on through natural selection. (mirrors modern theory)

Jean-Bapiste Lamarck's Theory

Organism change features during its lifetime in order to adapt to its environment, those adaptations are then passed to their offspring. (disproved theory)

Geological Time Scale - Define

A calendar of events in Earths History, subdividing time into eons, eras, periods, epochs and ages, based upon the colouration of rocks.

Fossil - Define

The remains of an organism of a past geological age that has been preserved in the crust.

Body Fossils - Define

Actual remains of an organism such as bones, teeth, shells, etc. Telling us the structure of their body

Trace Fossils - Define

Impressions left from the activity of an organism, indicating to scientists today their behaviour.

Transitional Fossils - Define

Fossils which demonstrate an intermediate form between an ancestor and its later decendants.

Fossilisation Steps - Define

R - Rapidly buried by sediment

U- Undisturbed, not eaten or scattered

D - Decomposition from oxygen and high temperatures is prevented.

Why do fossils commonly appear near water?

Many water sources offer optimal conditions for fossilisation with faster moving sediment, oftentimes being undisturbed and having low O2 levels and low temperatures.

How can we predict if two species are related evolutionarily?

Look at fossil records to look at genetic similarities in their body structure or in location and comparing DNA of the organisms which we have small samples of.

Biodiversity - Define

The variety of all life on Earth, caused by evolution and random mutation.

Common Ancestor - Define

A species who is the evolutionary ancestor of two specific species.

The Tree of Life/phylogenetic tree - Describe

A branching diagram that illustrates the evolutionary history and relationships among organisms, showing how species have diverged from common ancestors

What makes species distinct?

Any group of organisms that can interbreed to produce fertile offspring through reproductive isolation where a different species cannot produce fertile offspring.

E.g. The zonkey (zebra and donkey) can be born but cannot reproduce. Hence, zebras and donkeys are distinct species.