Elements and the Periodic Table 8th Grade Science Chapter 4 Elements and the Periodic Table 8th Grade Science

Introduction to Atoms Greek philosopher named __________ - proposed that matter is made up of tiny particles that cannot be made any smaller ________ - means “uncuttable” _____ - smallest particle of an element ___________ - formed in the 1600’s as a series of models developed from experimental evidence. Democritus “Atomos” Atom Atomic Theory

Atomic Theory As more experiments were conducted and evidence collected, the theory and models were revised. ________________ - John Dalton, English chemist, inferred that atoms had certain characteristics. Dalton’s atomic theory is still accepted today! Atoms were like smooth, hard balls that cannot be broken down Dalton’s Atomic Theory

Summary of Dalton’s Ideas page 103 All elements are composed of atoms that cannot be ______. All atoms of the same element are exactly alike and have the same ____. An atom of one element cannot be _________ into an atom of a different element – only rearranged. Every ________ is composed of atoms of different _________ combined in a specific ________. divided mass changed compound elements ratio

Thomson Model ___________ - 1897 atoms have negatively charged electrons embedded in a positive sphere. _______ - negatively charged particles JJ Thomson electrons

Rutherford and the Nucleus 1911 - ____________ - a student of Thomson, found evidence that contradicted Thomson’s model. ______________ - beam of positively charged particles aimed at a thin sheet of gold foil. Most of the particles passed through the foil as expected. However, a few particles were _______. Ernest Rutherford Gold Foil Experiment deflected

Conclusions from the Foil Experiment Since like charges _____ each other, Rutherford concluded that an atom’s _________ charges must be clustered in the _____ of the atom. ______ - center of the atom ________ - no mass ________ - positively charged particles that have mass and are located in the nucleus of the atom. repel positive center nucleus electrons protons

Rutherford’s Model

Bohr’s Model ___________ - 1913, Danish Scientist, student of both Thomson and Rutherford – electrons move around the nucleus in certain _____ based on energy levels. Bohr’s Model resembles planets orbiting the sun or layers of an onion. Neils Bohr orbit

Cloud of Electrons 1920’s – atomic model changed again Scientists determined that electrons DO NOT orbit the nucleus like planets. _________ can be anywhere in a cloudlike region around the __________. An _______ movement is related to its _________ - specific amount of energy that it has. ____________ affects the atoms reactions with other atoms. Electrons nucleus electrons Energy level Energy level

The Modern Atomic Model ___________ discovered another particle in the nucleus of atoms. _________ - particle discovered by Chadwick that has no electrical charge and nearly the same mass as _______. _______________ - consists of a nucleus that contains protons and neutrons surrounded by a cloudlike region of moving electrons. James Chadwick Neutrons Protons Modern Atomic Model

Particle Charges In an tom the number of ________ equals the number of __________. _________ have a positive charge and a ____ _________ have a negative charge and very little _______. _________ have neutral charge and a mass that equals that of protons. ________ charge of ________ equals the ________ charge of _________. protons Electrons mass Protons electrons mass Neutrons Positive Protons negative Electrons

Masses and Charges Charges balance making the atom neutral Particle Symbol Charge Relative Mass (amu) Proton p⁺ 1₊ 1 Neutron n Electron e⁻ 1₋ 1/1,836 Charges balance making the atom neutral Number of neutrons does not have to equal the number of protons Neutrons do not affect the charge of an atom because they have no charge Approximately 2,000 e⁻ equal mass of one proton.

Atomic Number Every atom of an element has the same number of _________. _____________ - number of protons in the nucleus of an atom. Atomic number identifies an _________. _______ - atoms with the same number of protons but a different number of neutrons. __________-sum of the protons and neutrons in the nucleus of an atom. protons Atomic Number element Isotopes Mass number

Patterns in the Elements _____________ - Russian scientist discovered a set of patterns that applied to all elements. Mendelev arranged the elements in order of increasing __________. ____________ - organization of the elements where the properties of the elements repeat in each row of the table. ___________ - Brittish scientist discovered a way to measure the positive charge on an atom’s nucleus – the atomic number. Dmitri Mendelev Atomic mass Periodic table Henry Moseley

Periodic Table of Elements After Moseley’s discovery, the periodic table was rearranged from ________ to _________. Properties of an element can be predicted based on its place in the ___________. Periodic table is arranged according to ___________ increasing from left to right. ________ - horizontal rows on the periodic table where the properties of the elements change in a set pattern. Atomic mass Atomic number Periodic table Atomic number periods

Organization of the Periodic Table Elements on the left side of the periodic table are _______________. Elements in the middle of the periodic table are ______________. Elements on the right side of the periodic table are _________________. ______ - 18 vertical columns or “families” on the periodic table with similar characteristics such as rate of reaction. (except lanthanides and actinides). Highly reactive metals Less reactive metals Metalloids and non-metals Groups

Reading the Periodic Table Each element in the periodic table has all of the following: ____________ - number of protons in the nucleus _____________ - 1 or 2 letter representation ____________ __________ - average mass of all of the isotopes of the element. Atomic Number Chemical Symbol Element Name Atomic Mass

Metals Physical properties of metals: ________ __________ - material can be hammered or rolled into flat sheets and other shapes. _______ - material can be pulled out or drawn into a thin wire __________ - ability of an object to transfer heat or electricity to another object. ___________ - metal that is liquid at room temperature shininess malleability ductility conductivity Mercury (Hg)

Chemical Properties of Metals _________ - the ease or speed of an element to combine or react to other elements and compounds. Metals usually react by losing ________ to other atoms. Sodium (Na) is very reactive where gold (Au) and platinum (Pt) are much less reactive. __________ - the destruction of a metal because of its reactivity. reactivity elements corrosion

Metals in the Periodic Table _______ of metals decreases from left to right on the periodic table. ____________ - metals in Group 1 on the periodic table that react with other elements by losing one ______. Alkali metals are never found in __________ elements in nature – only in compounds. ___________________ - two most important alkali metals – important for life processes. reactivity Alkali Metals electron uncombined Sodium(Na) and potassium (K)

Alkali Earth Metals ______________ - Group 2 on the periodic table that react with other metals by losing two electrons. Not as reactive as metals in __________ but more reactive than ,most other metals. Never found uncombined in nature. ______________________ - two most common alkali earth metals. Alkali Earth Metals Group 1 Magnesium (Mg) and Calcium (Ca)

Other Elements on the periodic table ____________ - elements in Group 3 through 12. These metals are hard and shiny, good conductors of electricity, less reactive than metals in Groups 1 and 2. ________ is an example of a very important transition metal. _______________ - only some are metals such as aluminum, tin and lead _________ - two rows of elements at the bottom of the periodic table. Transition Metals Iron (Fe) Groups 13, 14, and 15 Lanthanides

Lanthanides __________ - soft, malleable shiny metals with high conductivity. Lanthanides mix with other metals to form _____. _____ - mixture of a metal and at least one other element, usually another metal. _________ - only four occur naturally on earth – all others were created artificially. These elements are VERY unstable. Ex. Uranium Lanthanides alloys alloy Actinides

Synthetic Elements ____________ - elements that follow uranium that are not found naturally on Earth – when nuclear particles are forced to crash into one another. _____________ - powerful machines used by scientists to move atomic nuclei to very high speeds. Synthesized Particle accelerator

Non-metals and Metalloids Physical properties of non-metals: ______________ _____________________ Many non-metals are common elements on Earth ________non-metals are ______ at room temperature. ___________ - only non-metal that is liquid at room temperature Poor conductors Reactive with other elements Dull and brittle 10 of 16 gases Bromine (Br)

Chemical Properties of Non-Metals Atoms of non-metals usually _____ or ______ electrons with atoms that they react with. When metals and non-metals react, _________ move from the metal atoms to the non-metal atoms. Non-metals can also form compounds with other non-metals. gain share electrons

Families of Non-metals 1. _______________ - Group 14 only carbon is a non-metal. atoms that gain, lose, or share ____electrons when reacting with other elements. 2. ______________ - Group 15 contains two non-metals, nitrogen and phosphorous. These atoms usually gain, lose or share _______ electrons when reacting with other elements. 80% of the atmosphere is nitrogen gas (N₂) The Carbon Family four The Nitrogen Family three

Families of Non-Metals continued 3. _____________ - Group 16 contains three non-metals – oxygen, sulfur and selenium. Elements in the oxygen family usually gain or share ___ electrons. _________ is highly reactive – it can combine with nearly any other element. Oxygen is the ____ most abundant element in the atmosphere (Nitrogen is first) The Oxygen Family two oxygen most

The Halogen Family 4. ______________ - Group 17 contains flourine, chlorine, bromine, iodine, and astatine (not a non-metal). _______ means “salt forming”. Halogen atoms usually gain or share ____ electron when it reacts with other elements. All halogens are __________ and can be dangerous to humans. Many compounds that contain halogens can be useful to humans – salt, flourine in water, calcium chloride. The Halogen Family Halogen one Very reactive

Noble Gases __________ - elements in Group 18 that do not ordinarily form compounds because atoms of noble gases do not usually gain, lose, or share electrons. These gases are usually ___________. All of the noble gases exist in the Earth’s ___________. Noble gases were not discovered until late 1800’s because they are _______ and ________. Noble Gases unreactive atmosphere unreactive scarce

Hydrogen __________ - in the upper left corner of the periodic table. Hydrogen makes up more than ___ of the atoms in the universe. Hydrogen is rarely found as a ___________. Hydrogen (H) 90% Pure element

Metalloids ____________ - along the border between metals and non-metals. There are ___ metalloids and they have characteristics of both metals and non-metals. All metalloids are ____ at room temperature. Metalloids are also brittle, hard, somewhat reactive, varying ability to conduct heat and electricity ________ - most common metalloid Metalloids 7 solid Silicon (Si)

Semiconductors ____________ - substances that conduct electricity under some conditions but not under others. ________ are used as semiconductors because of their physical properties. Semiconductors are used to make _________, _____________, and ___________. Semi-conductors metalloids lasers Computer chips transmitters

Radioactive Elements _____________ - the atomic nuclei of unstable isotopes release fast moving particles and energy. _____________ - French scientist in 1896 discovered the effects of radioactive decay while he was studying a mineral that contained uranium. ___________ - named after __________ is the spontaneous emission of radiation by an unstable nucleus such as uranium. Radioactive Decay Henri Becquerel Marie Curie radioactivity

Types of Radioactive Decay Natural radioactive decay can produce ___________, ____________, and ___________. _________ - an alpha particle consists of two protons and two neutrons and is positively charged. The release of an alpha particle by an atom is decreases the atomic number by __ and the atomic mass by __ Alpha particles Beta particles Gamma rays Alpha decay 2 4

Beta Decay __________ - a neutron inside of the nucleus of an unstable atom changes into a negatively charged beta particle and a proton. __________ - fast moving electron given off by a nucleus during radioactive decay. Nucleus has one _____ neutron and one ____ proton – therefore, the atomic mass stays the same but the atomic number increases by __ Beta Decay Beta particle less more 1

Gamma Radiation _____________ - consists of high-energy waves – has no charge and does not cause a change in either atomic mass or atomic number. Gamma Radiation

Effects of Nuclear Radiation

Radioactive Isotopes