Regents Chemistry Lecture Notes for Topic I The Atom.

Regents Chemistry Lecture Notes for Topic I The Atom

Elements Elements are an extremely important part of our daily lives Each element is different and has different properties and behaviors Since ancient times, humans have used chemical changes to their advantage Example: processing of ores to produce metals for ornaments and tools

Elements and Changes early exp. Greeks were the first to try to explain why chemical changes occur. By 400 B.C., they had proposed that all matter was composed of four fundamental substances: fire, earth, water and air The next 2000 yearschemical history was characterized by alchemy

Elements early pioneers Robert Boyle (1627 1691) the first scientist to recognize the importance of careful measurements. Defined the term element in terms of experimentation; a substance was an element unless it could be broken down into two or more simpler substances

Elements How many Presently there are 110 different elements, of which 88 occur naturally (the rest have been made in laboratories) The elements vary tremendously in abundance For example, only 9 elements account for most of the compounds found in the Earths crust See pg. 87 tables 4.1 and 4.2

Elements The term element can used in different ways For example, element can mean a single atom of an element (microscopic view) Element can also mean a sample large enough to mass on a balance; this sample contains many atoms (macroscopic view)

Elements - symbols The names of chemical elements have many sources; often from Greek, Latin or German languages Example; the elemental name bromine comes from a Greek word meaning stench We use abbreviations (symbols) in place of the words

Your Assignment Read trace elements on pg. 88 and answer the following questions in complete sentences: Name and describe (4) trace elements and their impacts on our bodies What is Lithium used for? How does it affect our bodies? What did William Walsh discover? How? Are aluminum and fluoride good for us? Why or why not?

Regent Chemistry Evolution of atomic structure

Pre-Dalton the atom is mostly empty space and void : The Greeks! Said matter was made up of particles from four elemental substances : Earth, water, air and fire Daltons Postulates (proposed 1808) 1. All elements are composed of indivisible atoms 2. All atoms of a given element are identical Early Atomic Theory of Matter

Daltons Postulates 3. Atoms of different atoms are different; that is, they have different masses 4. Compounds are formed by the combination of atoms of different elements. Compounds are formed in definite proportions! Early Atomic Theory of Matter

Law of constant composition relatives numbers/kinds of atom are constant Law of conservation of mass total mass before = total mass after Law of multiple proportions (video) For example... What Daltons Law explains...

Same elements and mass before and after reaction

In the late 1890s J.J. Thomson cathode ray tube with magnetic fields cathode ray tube Observed nature of rays is the same regardless of identity of cathode material 1897 concluded that cathode rays are not rays but are particles with mass Generally accepted as the discovery of the electron -

J.J High voltage produces radiation within the tube know as cathode rays Movement in tube can be seen as cathode rays cause certain materials to fluoresce Can be deflected by magnetic fields

Shortly after...William Thomson aka Lord Kelvin Concluded atom is a large positive sphere with electrons floating around like raisons in pudding

Ernest Rutherford..the famous exp. Disproved Thomsons Plum Pudding Model How?? Alpha and Beta particle scattering experiment (video) The famous gold foil experiment (video) Coming up next..modern atomic structure

Your Assignment Write an essay using the information from this lecture and pg 90-96 in your textbook. Your essay should be approximately 500 words in length and compare/contrast the contributions of JJ Thomson, Lord Kelvin and Ernest Rutherford

Regents Chemistry Modern Atomic Theory

Nucleus electrons The nucleus contains A positive charge.. Electrons surround the nucleus in a cloud

Modern Atomic Theory Modern atomic theory is based on two models The Bohr Model (planetary model) The Wave Mechanical Model

The Bohr Model Neils Bohr proposed a model of the atom with a dense, positive charge in the center and electrons surrounding the nucleus in specific orbits.. Ask me!

Location of electrons energy levels Electrons are in specific levels according to the amount of energy they contain There are maximum numbers of electrons for each level Electrons can jump from one level to another by absorbing or emitting photons of energy..

Location of electrons We can identify an elements electrons distribution by looking at the periodic table These number describe how many electrons are in each level

Jumping of Electrons Check this outwhat happens when we excite the electrons of specific metals? Why do we see a color? Why do different metals show different colors? Can we get any other info from this demo?

Jumping levels Electrons in a non excited state are said to be in the ground state We just observed how to excite these electrons.. But how does this change an elements electrons distribution Check out your PT

Spectral Lines When electrons are emitted or absorbed from specific elements, we see the result in two ways.. Emission Spectra Absorption Spectra

Emission and Absorption Spectra

The Wave Mechanical Model Most current model of electron behavior Proposes electrons are in orbitals, which are regions of high probability of finding an electrons Also called the electron cloud model Why this model?because of wave behavior of electrons

Classwork Read the attached article regarding protons, neutrons and electrons. Answer the questions on the handout using this information. Modern Atomic Theory

Regents Chemistry The Structure of the Atom

The Nucleus A dense centered nucleus contains protons and neutrons Protons are (+) Neutrons have no charge These have a mass of 1 amu and make up most of the mass of an atom This mass is called an elements atomic mass

Subatomic Particles We measure the mass of protons and neutrons in atomic mass units (amu) The atomic mass unit is based on 1/12 the mass of the C 12 isotope The protons define an element This is called an elements Atomic Number

Isotopes WE CAN NEVER CHANGE AN ELEMENTS ATOMIC NUMBER (# p) We does vary is an elements number of neutrons Atoms of the same element that have different numbers of neutrons are called Isotopes C 14 and C 12 are isotopes

Isotopes cont An Isotope is an atom that looses or gains neutrons. It is thus lighter or heavier than the base atom of the element.

Average Atomic Mass The atomic mass listed on the Periodic table is actually the average of all known atomic masses for that element How do we do thiseasy!

Atomic Weights and Isotopes Multiply the exact weight x % abundance for Each isotope and then add them up!

Regents Chemistry Types of Matter

What is Matter? Matter is the stuff of which the universe is composed Anything that has mass and occupies space is considered matter!

Mixtures and Pure Substances A mixture is something that has variable composition. Example: soil, cereal, air A pure substance will always have the same composition. Pure substances are elements or compounds. Example: pure water, table salt, carbon

Mixtures For Example: AIR Mixture of oxygen nitrogen, carbon dioxide Argon, water, others Elements, which are pure substances Compounds, which are pure substances

Elements and Compounds Pure substances have an invariable composition and are composed of either elements or compounds. Elements "Substances which cannot be decomposed into simpler substances by chemical means". Compounds Can be decomposed into two or more elements.

Elements Elements are the basic substances out of which all matter is composed. Everything in the world is made up from only 110 different elements. 90% of the human body is composed of only three elements: Oxygen, Carbon and Hydrogen Elements are known by common names as well as by their abbreviations (symbols).

Compounds Compounds are substances of two or more elements united chemically in definite proportions by mass. The observation that the elemental composition of a pure compound is always the same is known as the law of constant composition (or the law of definite proportions). For Example...

For example, pure water is composed of the elements hydrogen (H) and oxygen (O) at the defined ratio of 11 % hydrogen and 89 % oxygen by mass. Good Old H 2 O Worksheet

Classification of Mixtures Homogeneous Mixtures are the same throughout (a single phase). ex: table salt and water, air, brass Heterogeneous Mixtures contain regions that have different properties from those of other regions (more than 1 phase). ex: sand in water, cereal Phase - area of uniform composition

Examples of Heterogeneous Mixtures Sand on a beach Cereal sand in water sugar in lemonade Most of the time you can see the different substances, hence the mixtures are said to be not well mixed and can be separated physically

Examples of Homogeneous Mixtures, also called Solutions Air Table salt in water Solution of Na 2 SO 4 You cannot see the different substances in the mixture (solution) - can be separated by chemical or physical means

Means of Separation Use a magnet - physical Ex: Iron and sand mixture Distillation - physical Ex: salt and water mixture see distillation apparatus Filtration - physical Ex: sand and water mixture Electrolysis - chemical Ex: water - see video - worksheet

Identify each of the following..

Regents Chemistry Lecture Notes for Topic I The Atom.

Documents

elements elements

different elements

atom slide

trace elements

elements account

alchemy slide

tools slide

reaction slide