Chem Exam 1

What is Chemistry?

The study of matter and changes it undergoes

Laws

Summarize what happens

Mega

1 million

Kilo

1000

Deci

0.1 / 10 in 1

Centi

0.01 / 100 in 1

Mili

0.001 / 1000 in 1

Micro

0.000001 / 1 million in 1

1 inch = how many cm?

2.54 cm

1 mL =

1 cm³

1 lb= how many g?

453.6 g

Accuracy

How close a measured value is to a true / correct value

Precision

With multiple measurements, how close are those measurements to eachother

Uncertainty

Smallest division in the instrument divided by 2

Kelvin= Celsius plus what

273.2

Density formula

Mass/volume

g/cm³ or g/mL

Matter

Anything occupying space and having mass

Solid

Rigid

Has fixed volume and shape

Liquid

Has definite volume but no specific shape

Takes shape of container

Gas

Has no fixed volume or shape

Takes shape and volume of container

Physical Properites

Characteristics of matter that can be changed without changing composition

Directly observable

Chemical properties

A substances ability to form new substances

Characteristics that determine how composition of matter changes as a result of contact with other matter or influence of energy

Characteristics that describe behavior of matter

Physical Change

Change in form, not composition

Chemical Change

A substance becomes a new substance with different properties and composition

Chemical reaction

Chemical Reaction

One substance changes to another by reorganizing the way atoms are attached to eachother

Burning = chemical change

Element

Can’t be broken down any further by chemical methods

Anything in periodic table

All matters made of elements

Compound

Combo of elements that can be broken down into elements by chemical methods

Always contains atoms of different elements

Always same composition / combos of atoms

Pure substance

Always same composition

Either element or compound

Mixtures

2 or more pure substances

More that 1 element or compound hanging out in same place

Can be separated into pure substances (elements and/or compounds)

Homogeneous Mixture

Mixture with same composition throughout mixture

Evenly distributed

Visibly indistinguishable parts

A solution

Composition doesn’t vary throughout mixture

Heterogeneous Mixture

Visibly distinguishable parts

Not uniformly distributed

Energy

Ability to do work or produce heat

That which is needed to oppose natural forces

Potential energy

Energy due to position or composition

Kinetic energy

Energy due to motion of the object

Depends on mass and velocity

Heat

Involves transfer of energy between 2 objects due to temperature differences

Heat is the way in which thermal energy is transferred from a hot object to a colder one

Heat is Energy

Work

Force acting over a distance

State function

Property that doesn’t depend in any way on systems past or future (only depends on present)

Changes don’t depend on pathway —> and goal is the same

Energy is a state function; work and heat aren’t

Regardless of path took, ended in same place

Temperature

A measure of the random motions of the components of a substance

Hot= more motion

Cold=less motion / kinetic energy

System

Part of the universe which we focus on

Surroundings

Everything outside system

Endothermic process

Energy going into process/reaction

Energy goes up during reaction —> products energy greater than reactants energy

Energy comes from surroundings and system absorbs heat energy from surroundings

Exothermic process

Energy exiting/leaving process/reaction

Energy goes down during reaction —> products energy less than reactants energy

Energy goes to surroundings and system releases heat to surroundings

Thermodynamics

Study of energy/motion of energy

Law of conservation of energy is often called law of thermodynamics

Energy of a system formula

The sum of kinetic and potential energy particles in the system

Delta E= q (heat) + w (work)

In the endothermic process is q positive or negative?

Positive because energy is going into process to system and + = increase

In the exothermic process is q positive or negative?

Negative because energy is going out of the system and - = decrease

What’s it mean if w is positive

Surroundings do work on the system

Something ELSE (the surroundings) is pushing down on the gas

What’s it mean if w is negative?

Energy is moving away and trying to escape so w is negative

Gas is pushing outward and outward= negative

Robert Boyle

First real chemist

Performed quantitative elements

Defined element as something that couldn’t be broken further

Law of Comdtant composition

Compound always has same composition, despite origin

John Dalton

English scientist who is known for atomic theory

Atomic theory

Elements made up of atoms

In each element the atoms in it are identical and atoms in different elements are different in some fundamental way

Compounds are formed when atoms of elements come together. A given compound always has the same relative number and goes of atoms

Atoms of one element can combine with atoms of other elements to form compounds

Atoms can’t be broken down any further

J.J. Thomson

Investigated the existence of electrons using cathode ray tubes

He applies high voltage in a partially evacuated tube and a ray produced at the cathode

The ray was repelled by negative pole of applied electric field - particles were negatively charged

Deduced that atoms must also contain a positive charge

William Thomson

Plum pudding model

Electrons scattered within atom to counterbalance the positive charge of atom

Ernest Rutherford

Carried out Gold Foil Experiment to test Thomason’s plum pudding model

He directed alpha particles at a sheet of gold atoms (gold foil)

He hypothesized that : particles coming out the machine were gonna be big so when they interacted with the foil the alpha particles (since electrons are small) should pass straight through the foil unaltered in their path of motion

Results: many passed through but there was also deflection

Discovered positive charge must be in a specific place→ Given credit for discovering atom nucleus

Gold foil experiment led to

Nucleus with dense center of positive charges

negative charges traveling at a far distance from the nucleus

James Chadwick

Discovered neutron and that it was neutral and in nucleus with protons

Most weight of the atom comes from

Protons and neutrons

A / Z X model

A is mass #

Z is atomic #

X is element symbol

Atomic #

Number of protons

Defined the elements

Cannot be changed under normal chemical means

Mass #

Represents the number of protons and neutrons

Can be different for the same element (Isotopes) because the amount of neutrons can differ

Always bigger than atomic # (excluding Hydrogen)

Isotopes

Atoms with same number of protons but different number of neutrons

Show almost identical chemical properties because the chemistry of atoms is due to electrons

In nature most elements have several isotopes

Metals

Left side of stair case

Non metals

Right side of staircase + Hydrogen

Metaloids

Elements in contacts with staircase and have properties of both metals and non metals

Excluding Aluminum and Boron

1A / Column 1

Alkali metals

2A / Column 2

Alkaline earth metals

7A / Column 17

Halogens

8A / Column 18

Noble Gases

Periods

Horizontal rows of elements

7 of them

Physical properties of metals

Efficient conduction of heat and electricity

Malleability (Flattenable)

Ductility (can be pulled into wires)

Shiny/Lustrous appearance

Metals tend to ___ electrons to form ___ ions

Lose ; positive

More positives than negatives giving it an overall negative charge

Nonmetals tend to ___ electrons to form ___ ions

Gain ; negative

Why are elements not generally found in combined forms. What group is excluded?

Most elements are very reactive

Noble metals such as gold, platinum, and silver which are Collumn 11 and Noble gasses Column 18

7 Diatomic Molecules

Elmer’s that exist naturally as two identical atoms

Never (Nitrogen) have (Hydrogen) fear (fluorine) of (oxygen) ice (iodine) cold (chlorine) beer (bromine)

Allotropes

Different forms of a given element

Different 3d shapes

1kcal=? Cals

1000

1 cal = how many J

4.184

Scientific Method

A systematic process scientists use to investigate questions and solve problems using observations, experiments, and evidence.

Observation

Information gathered about something using the senses or scientific instruments.

SI Unit length

Meters

SI unit Mass

Kg

SI Unit time

seconds

SI Unit temp

Kelvin

SI units amt. of subtance

Mole

Specific Heat formula and what each variable means

q=mc(delta)T

q= heat/energy

m= mass (g)

c= specific heat capacity of the element

(delta)T= temp difference

Whats specific heat capacity measured with?

J/g°C.

Calorie

Amount of energy (heat) required to raise temp of one gram of water to 1 degree celsius

What is specific heat capacity?

The amount of energy required to change the temp of a mass of 1 gram of a substance by one celsius

Change in enthalpy

Heat flow associated with a chem process

State function

(Delta)H=q at constant pressure

Units of energy (cal, J, mainly kJ)

Calorimetry

Change in Enthalpy (Delta)H is measured using a calorimeter and often in cals

Ions

Atoms with same # of protons but diff number of electrons

Charged species

Cations

Formed when electrons are lost

Element + Ion (Ex Fluorine Ion)

Metals love losing electrons so they form cations

Anions

Formed when electrons are gained

Nonmetals gain electrons to form anions

Change ending of element to IDE+ion (Ex Nitride Ion)

Left side of periodic table charge

Positive

Right side of periodic table charge

Negative

Ionic Compounds

Ions combine to form ionic compounds

Electrically neutral

Ionization energy def and periodic trend

Energy required to remove an electron from an element

Increases up and right

Atomic size periodic trend

Bigger going left and down