Jee mains has not officially announced the weightage of each chapter and subject as from less important chapters questions can come like the 2017jee mains paper.For syllabus related details you can visit the below given link :
All the best!:)
You can consider below details for the same -
Maths - Inverse Trigonometric Functions Weightage: 2% Circles and Family of Circles Weightage: 6% Sequence and Series Weightage: 5% Applications of Derivative Weightage: 4% Limit and Continuity Weightage: 3% Matrices and Determinants Weightage: 4% Straight Lines and Pair of Straight Lines Weightage: 2% 3-D Geometry Weightage: 5% Probability and Statistics Weightage: 7% Vector Algebra Weightage: 5% Integration Weightage: 8% (Definite + Indefinite integration) Complex Numbers Weightage: 5% Parabola Weightage: 3% Trigonometric Ratios Weightage: 3% Logarithms Weightage: 1% Quadratic Equations Theory of Equations Weightage: 5% Sets, Relations and Functions Weightage: 4% Differentiation 2% Permutation and Combination Weightage: 2%. You should study this properly as concepts from this section will be needed in Probabilty Binomial Theorem Weightage: 1% Locus Hyperbola Weightage: 2% Ellipse Weightage: 2% Fundamentals of Mathematics Solution of Triangle 1%.
Chemistry - General Organic Chemistry 9% Alcohol Phenol Ether 7% Redox reactions 6% Chemical Bonding 5% Coordination Compound 5% P-Block Elements 5% S-Block Elements 5% Aldehyde Ketone 5% Solutions 5% Solid State 5% Chemical Thermodynamics 5% Ionic Equilibrium 3% Chemical Equilibrium 3% Surface Chemistry 3% Atomic Structure 2% Gaseous State 2% Transition Elements 2% Polymers 2% Nuclear Chemistry 2% Chemical Kinetics 2% Mole Concepts 2% Amines and Diazonium Salts 2% Biomolecules 2% Alkanes, Alkenes and Alkynes 2% Electrochemistry 2%.
Physics - Units and Dimensions Weightage: 2% Measurement of Errors Weightage: 2% Vectors Kinematics Weightage: 1% Newtons Laws of Motion Weightage: 4% Friction Work, Energy and Power Weightage: 5% Electrostatics Weightage: 6% Current Electricity Weightage: 7% Wave Optics Weightage: 5% Ray Optics Weightage: 6% Centre of Mass, Momentum and Collision Weightage: 5% Rotational Dynamics Weightage: 4% Simple Harmonic Motion Weightage: 5% Fluid Mechanics Weightage: 2 5%. Wave Motion and String Waves Weightage: 5% Magnetism Weightage: 6% Heat & Thermodynamics Weightage: 6%.Nuclear Physics Weightage: 5% Modern Physics Weightage: 5%, Circular Motion Weightage: 1% Gravitation Weightage: 1% Properties of Matter, Elasticity Weightage: 2% Sound Waves Electromagnetic Induction Weightage: 3% Alternating Current Weightage: 1% Semiconductors and Electronic Devices 5%.
Good luck :)