Atoms: Inside Out PDF

Atoms: Inside Out Essential question  What is an atom and how did the ideas about it evolve?  What are the particles that make up an atom?  How do these components differ from each other?  How are these components arranged inside the atom?  molecule  Molecule, a group of two or more at...

Atoms: Inside Out Essential question  What is an atom and how did the ideas about it evolve?  What are the particles that make up an atom?  How do these components differ from each other?  How are these components arranged inside the atom?  molecule  Molecule, a group of two or more atoms that form the smallest identifiable unit into which a pure substance can be divided and still retain the composition and chemical properties of that substance. Who are these men? In this lesson, we’ll learn about the men whose quests for knowledge about the fundamental nature of the universe helped define our views.  It was understood that bonds had direction, rigidity, and a certain degree of independence from molecule to molecule. The discovery of the electron in 1897 by English physicist Joseph John Thomson (1856–1940) immediately linked electrons with covalent bonding.  Covalent bond= sharing of electrons  Democritus This is the Greek philosopher Democritus who began the search for a description of matter more than 2400 years ago. He asked: Could matter be divided into smaller and smaller pieces forever, or was there a limit to the number of times a piece of matter could be divided?  Believed universe made of indivisible units called atoms He named the smallest piece of matter “atomos,” meaning “not to be cut.” Aristotle said “He’s a quack!!!” Atomos § To Democritus, atoms were small, hard particles that were all made of the same material but were different shapes and sizes. § Atoms were infinite in number, always moving and capable of joining together.  This theory was ignored and forgotten for more than 2000 years! Took 2000 years to be proved right!  Dalton’s Atomic Theory John Dalton (1766 – 1844) Wrote the first atomic theory In the early 1800s, the English Chemist John Dalton performed a number of experiments that eventually led to the acceptance of the idea of atoms.  Wrote the first atomic theory 1. All elements are composed of tiny indivisible particles called atoms 2. Atoms of the same element are identical. -Atoms of any one element are different from those of any other element. 3. Atoms of different elements combine in simple whole-number ratios to form chemical compounds. Ex. H2O  4. In chemical reactions, atoms are combined, separated, or rearranged – but never changed into atoms of another element. This theory became one of the foundations of modern chemistry. Supported by this law: Law of conservation of mass- Matter cannot be created nor destroyed. The “Billiard Ball” Model  proposed by John Dalton in 1804  thistheory proposed that matter was composed of small, spherical particles  butevidence was later gathered that matter was composed of even smaller bits  New Evidence  during the 1900s evidence was discovered regarding charges:  atoms have positive (Rutherford’s contribution) and negative (Thomson’s contribution) parts  charges interact:  “Like charges repel; Unlike charges Attracts”  as a result, revisions to Dalton’s model had to be made  FYI……….Isotopes Dalton was wrong about all elements of the same type being identical Atoms of the same element can have different numbers of neutrons. Thus, different mass numbers. These are called isotopes.  Frederick Soddy Frederick Soddy (1877-1956) proposed the idea of isotopes in 1912 (note this was close to 30 years after Dalton’s original idea)  Isotopes are atoms of the same element having different masses, due to varying numbers of neutrons.  Soddy won the Nobel Prize in Chemistry in 1921 for his work with isotopes and radioactive materials. Thomson’s Plum Pudding Model In 1897, the English scientist Joseph John Thomson provided the first hint that an atom is made of even smaller particles. Thomson Model Where did they come  This surprised from? Thomson, because the atoms of the gas were uncharged. Where had the negative charges come from? Thomson concluded that the negative charges came from within the atom. A particle smaller than an atom had to exist. The atom was divisible! Thomson called the negatively charged “corpuscles,” today known as electrons. Since the gas was known to be neutral, having no charge, he reasoned that there must be positively charged particles in the atom. But he could never find them. Thomson Model  Heproposed a model of the atom that is sometimes called the “Plum Pudding” model.  Atoms were made from a positively charged substance with negatively charged electrons scattered about, like raisins in a pudding.  Thomson: “Plum Pudding” or “Chocolate Chip Cookie” Model  using available data on the atom, J.J. Thomson came up with the idea of having charges embedded with Dalton’s Billiard Balls  Also used cathode ray experiment to discover the existance of the electron positive negative (evenly distributed) “chocolate” “dough” part note: this model kept Dalton’s key ideas intact Discovery of the Electron In 1897, J.J. Thomson used a cathode ray tube to deduce the presence of a negatively charged particle: the electron Click on me: http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/ruther14.swf Conclusions from the Study of the Electron: A. Cathode rays have identical properties regardless of the element used to produce them. All elements must contain identically charged electrons. B. Atoms are neutral, so there must be positive particles in the atom to balance the negative charge of the electrons C. Electrons have so little mass that atoms must contain other particles that account for most of the mass Mass of the Electron Mass of the electron is 9.11 x 10-28 g Electron Facts: Mass: 9.109 x 10-28 grams Symbol: e- Rutherford’s Gold Foil Experiment  In 1908, the English physicist Ernest Rutherford was hard at work on an experiment that seemed to have little to do with unraveling the mysteries of the atomic structure.  Rutherford  Discovered the Nucleus and the Positive Protons  Surmised atoms are made of mostly empty space  Didn’t know about the Neutrons  Famous Gold Foil Experiment  Click on me: http://www.mhhe.com/physsci/chemistry/essentialchemi stry/flash/ruther14.swf  Rutherford’s experiment Involved firing a stream of tiny positively charged particles at a thin sheet of gold foil (2000 atoms thick) Ernest Rutherford (movie: 10 min.)  Rutherford shot alpha () particles at gold foil. Zinc sulfide Thin gold foil screen Lead block Radioactive path of invisible substance -particles Most particles passed through. So, atoms are mostly empty. Some positive -particles deflected or bounced back! Thus, a “nucleus” is positive & holds most of an atom’s mass.  Most of the positively charged “bullets” passed right through the gold atoms in the sheet of gold foil without changing course at all.  Some of the positively charged “bullets,” however, did bounce away from the gold sheet as if they had hit something solid. He knew that positive charges repel positive charges.  This could only mean that the gold atoms in the sheet were mostly open space. Atoms were not a pudding filled with a positively charged material.  Rutherford concluded that an atom had a small, dense, positively charged center that repelled his positively charged “bullets.”  He called the center of the atom the “nucleus”  The nucleus is tiny compared to the atom as a whole. Rutherford  Rutherford reasoned that all of an atom’s positively charged particles were contained in the nucleus. The negatively charged particles were scattered outside the nucleus around the atom’s edge.  His model became known as empty space model or Proton Facts: Mass: 1.672 x 10-24 grams Symbol : p+ Bohr Model  In 1913, the Danish scientist Neils Bohr proposed an improvement. In his model, he placed each electron in a specific energy level. Bohr Model  According to Bohr’s atomic model, electrons move in definite orbits around the nucleus, much like planets circle the sun. These orbits, or energy levels, are located at certain distances from the nucleus.  “planetary model” What About Me? Neutron Facts:  James Chadwick: proved the existence of neutrons in 1932  Charge: no charge, as in zero  Mass: 1.675 x 10 - 2 4 grams Symbol : n  Description of atom Model Democritus atoms were small, hard particles that were all made of the same material but were different shapes and sizes. John Dalton proposed that matter was composed of small, Billiard ball/ spherical particles Hard sphere model Joseph John Thomson provided the first hint that an atom is made of Plum Pudding model even smaller particles. leads to the discovery of electron Ernest Rutherford all of an atom’s positively charged particles Empty space model/ were contained in the nucleus. The negatively Nuclear model charged particles were scattered outside the nucleus around the atom’s edge. (Gold Foil Experiment) - proton (positively charge) Neils Bohr In his model, he placed each electron in a Bohr’s model /Planetary model specific energy level.  Inside the atom Nucleus- is a positively charged region at the center of the atom. Consist of 2 sub-atomic particles protons (positively charge) and neutrons (neutral in electric p+ charge) neutrons Electrons- is a negatively charge particles Sub-atomic particles of an atom: NOTE: Proton- carries positive charge Atoms in their most stable state are Electron- carries a negative charge neutral with an equal number of Neutron- does not carry any charge protons and electrons. TABLE 4.1 Properties of the proton, the neutron, and the electron Relative mass Location in Particle Actual mass (g) charge (amu) the atom Proton (p+ ) 1.672 X 10-24 1.007 +1 nucleus Neutron(n ) 1.675 X 10-24 1.008 0 nucleus Outside Electron(e-) 9.109 X 10-28 5.45 X 10-4 -1 nucleus Answer this: What are the particles that make up an atom? How do these components differ from each other? How are these components arranged inside the atom? Why we need to know the number of protons and electrons of an atom?  1. The numbers of in the nucleus, knows as the atomic number “primarily determines where that atom fits on the periodic table. The number of protons in the nucleus also defines in large part the characteristics of an atom- is it a gas or a metal.  2. Protons in the nucleus mostly determines the mass of an atom.  3. determines the chemical reaction of an atom. (either it will accepts electrons or gave in electrons) Remember this:  Atoms contain particles with positive and negative charges.  Atom- comes from a Greek word ATOMOS, means indivisible; not to be cut  Sub-atomic particles of an atom:  Proton- carries positive charge  Electron- carries a negative charge  Neutron- does not carry any charge  NOTE:  Atoms in their most stable state are neutral with an equal number of protons and electrons. Thank you!!!